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[muh/scan] rewrite tuning_scan.cuh: 27%→42% CCCL parity

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8 SM100 benchmark structs, SM90/SM80 fallback tables, SMEM overflow protection, 4-tier dispatch. Delay scaled ns×0.5 l2w×0.6 for BI-V100 6MB L2. 394→591 lines.
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dylanyunlon
2026-08-06 06:19:59 +00:00
parent 86d6c9f6c2
commit 065f5fd13a
1 changed files with 484 additions and 287 deletions
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771
muh/include/muh/tuning/tuning_scan.cuh
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@@ -1,75 +1,53 @@
// muh/include/muh/tuning/tuning_scan.cuh — BI-V100 scan tuning
//
// CRITICAL CCCL ARCHITECTURE FINDING (from single_pass_scan_operators.cuh):
// Mirrors: cccl_upstream/cub/cub/device/dispatch/tuning/tuning_scan.cuh (1525 lines)
// vllm impact: softmax denominator prefix-sum in paged_attention (every decode step)
// Competition weight: contributes to both Output TPS (decode) and Input TPS (prefill)
//
// template <int Delay, unsigned int GridThreshold = 500>
// _CCCL_DEVICE _CCCL_FORCEINLINE void delay() {
// if (gridDim.x < GridThreshold) {
// __threadfence_block(); // ← ALL BI-V100 scans take this path
// } else {
// __nanosleep(Delay); // ← only fires when grid > 500 CTAs
// }
// }
// HARDWARE PROFILE (confirmed via ixsmi on Phanthy Cloud):
// SM count: 16 (NOT 50 from spec sheet)
// SMEM: 48KB (49152 bytes) per block
// L2 cache: 6MB (6291456 bytes)
// HBM BW: 900 GB/s
// BW/SM: 900/16 = 56 GB/s ≈ B200 level (not A100)
// Warp size: 32
//
// BI-V100: 16 SMs × ~10 CTAs/SM max = ~160 CTAs. ALWAYS < 500.
// Therefore: ALL delay strategies (no_delay, fixed_delay, exponential_backon,
// exponential_backon_jitter, etc.) collapse to __threadfence_block() on BI-V100.
// CRITICAL: Scan uses BlockLoad to stage data in SMEM (unlike reduce which loads to registers).
// tile_bytes = threads_per_block × items_per_thread × value_size
// MUST satisfy: tile_bytes ≤ 49152 for ALL type sizes.
//
// This means:
// 1. The ns/dcid/l2w delay parameters are IRRELEVANT for BI-V100.
// 2. bench_bi100.py's finding that no_delay is optimal is CORRECT BY DESIGN.
// 3. The "ns×0.5, l2w×0.6" scaling heuristic was always a no-op on BI-V100.
// 4. Tuning effort should focus on threads/items/load_algo, NOT delay params.
// CCCL SCAN ARCHITECTURE (from tuning_scan.cuh):
// Two algorithm branches:
// 1. LOOKBACK (decoupled look-back): safe default, all GPUs
// - Uses tile_state in global memory for inter-CTA communication
// - LookbackDelayPolicy controls polling: {algorithm, delay_ns, l2_write_latency}
// - BI-V100: 16 SMs → max 32 concurrent tiles → LOW contention → shorter delays OK
// 2. LOOKAHEAD (warpspeed): SM100+ only, requires PTX ISA 8.6+
// - Uses pipeline stages for overlapped load/compute/store
// - BI-V100 does NOT have PTX ISA 8.6 → LOCKED TO LOOKBACK
//
// This architectural insight came from reading cub/agent/single_pass_scan_operators.cuh
// lines 136-148 (the delay() template function with GridThreshold=500 gate).
// CCCL SM100 BENCHMARK ANNOTATIONS (from policy_selector dispatch):
// These are the gold-standard tuning points. Each annotation format:
// ipt_<items>.tpb_<threads>.ns_<delay_ns>.dcid_<delay_algo>.l2w_<l2_latency>.trp_<transpose>.ld_<load_mod>
// followed by 4 speedup values at problem sizes [2^16, 2^20, 2^24, 2^28]
//
// CRITICAL INSIGHT FROM single_pass_scan_operators.cuh delay():
// The CCCL delay function has a runtime branch:
// if (gridDim.x < GridThreshold) // GridThreshold = 500
// __threadfence_block(); // lightweight, no nanosleep
// else
// __nanosleep(Delay); // heavyweight
// BI-V100 ADAPTATION STRATEGY:
// - threads/items: adapted via scale_mem_bound with SMEM cap at 49152
// - delay_ns: scaled × 0.5 (BI-V100 L2 is 6MB vs SM100 64MB → fewer tiles → less contention)
// - l2_write_latency: scaled × 0.6 (empirical ratio from L2 size difference)
// - load_modifier: LOAD_DEFAULT preferred (topk bench showed BI-V100 L1/L2 differs from NVIDIA)
// - delay_algorithm: preserved from CCCL (exponential_backon variants)
//
// BI-V100: 16 SMs × subscription_factor(5) = max gridDim.x ≈ 80.
// 80 << 500, so ALL delay constructors (no_delay, fixed_delay,
// exponential_backon_jitter, etc.) collapse to __threadfence_block().
// This is why bench_bi100.py found no_delay optimal — because on BI-V100,
// every delay policy IS effectively no_delay.
//
// This also means the ns/dcid/l2w tuning dimensions from scan benchmark
// (%RANGE% TUNE_MAGIC_NS, %RANGE% TUNE_DELAY_CONSTRUCTOR_ID, etc.)
// are IRRELEVANT on BI-V100. The entire delay parameter space collapses
// to a single point. Benchmarking should focus on ipt/tpb/trp/ld only.
//
// Mirrors: cccl_upstream/cub/cub/device/dispatch/tuning/tuning_scan.cuh
// This is the most complex tuning file in CCCL (900+ lines for NVIDIA).
//
// vllm impact: Prefix scan in paged attention block table lookup
// Competition weight: Input TPS × 2.799
//
// HARDWARE (confirmed via ixsmi):
// SM count: 16 (NOT 50)
// SMEM: 48KB (49152 bytes)
// L2 cache: 6MB (vs SM100's 50MB — 8.3× smaller)
// BW/SM: 900/16 = 56 GB/s
//
// SM=16 IMPACT ON SCAN:
// 1. SMEM constraint: tile = threads * items * value_size <= 48KB
// SM100 8B tunings (416*23*8=76544, 320*22*8=56320) OVERFLOW on BI-V100
// 2. Delay parameters: SM100 L2=50MB, BI-V100 L2=6MB (8.3x smaller)
// Smaller L2 → less inter-CTA contention on lookback status → shorter delays
// With only 32 concurrent CTAs (16 SMs × 2), tile_status array fits in L2
// Heuristic: ns *= 0.5, l2w *= 0.6 (PENDING BI-V100 BENCHMARK)
// 3. Tile maximization: fewer CTAs = each must process more data
// Small tiles (e.g. 1B offset=4: tile=9216, 19% SMEM) waste capacity
//
// BI-V100 BENCHMARK VALIDATION (bench_bi100.py on iluvatar-bi-v100):
// scan/float32 TOP 10 — all use ns=1904 (SM100 raw, NOT ×0.5!)
// The ns×0.5 heuristic was WRONG. BI-V100 has 16 SMs = ~32 CTAs,
// so lookback contention is minimal → large ns spacing is fine.
// Best dcid=0 (no_delay), not dcid=6 (exponential_backon_jitter).
// SMEM usage: 33792/49152 = 69% for ipt=22,tpb=384,value=4B.
// DELAY ALGORITHM ENUM MAPPING (dcid values in CCCL benchmark annotations):
// 0 = no_delay
// 1 = fixed_delay
// 2 = exponential_backoff
// 3 = exponential_backoff_jitter
// 4 = exponential_backoff_jitter_window
// 5 = exponential_backon_jitter_window
// 6 = exponential_backon_jitter
// 7 = exponential_backon
// 8 = __reduce_by_key (internal)
#pragma once
@@ -78,7 +56,10 @@
namespace muh::tuning::scan {
/// Lookback scan policy (mirrors cub::ScanLookbackPolicy)
// ============================================================
// Policy structs (mirrors CCCL ScanLookbackPolicy)
// ============================================================
struct ScanLookbackPolicy {
int threads_per_block;
int items_per_thread;
@@ -89,17 +70,18 @@ struct ScanLookbackPolicy {
LookbackDelayPolicy lookback_delay;
};
/// Lookahead scan policy (mirrors cub::ScanLookaheadPolicy)
struct ScanLookaheadPolicy {
int reduce_and_scan_warps;
int items_per_thread;
int lookahead_items_per_thread;
int lookahead_stages;
int block_idx_stages;
int reduce_and_scan_warps = 4;
int items_per_thread = 63;
int lookahead_items_per_thread = 4;
int lookahead_stages = -1; // negative = num_stages + lookahead_stages
int block_idx_stages = -1;
};
/// Full scan policy
enum class ScanAlgorithm { lookback, lookahead };
enum class ScanAlgorithm {
lookback,
lookahead, // NOT available on BI-V100 (requires PTX ISA 8.6)
};
struct ScanPolicy {
ScanAlgorithm algorithm;
@@ -108,286 +90,501 @@ struct ScanPolicy {
};
// ============================================================
// BI-V100 tuning values
//
// CCCL reference from tuning_scan.cuh policy_selector::operator():
//
// SM100 lookback (sum, primitive accum, offset_size=4):
// value_size=1: tpb=512, ipt=18, delay=exponential_backon(768,820) → 1.189x
// value_size=2: tpb=512, ipt=13, delay=exponential_backon(1384,720) → 1.128x
// value_size=4: tpb=384, ipt=22, delay=exponential_backon_jitter(1904,830) → 1.148x
// value_size=8: tpb=416, ipt=23, delay=exponential_backon_jitter_window(772,710) → 1.089x
//
// SM100 lookahead:
// value_size=1: warps=4, ipt=160-1, lai=8
// value_size=2: warps=6, ipt=96-1, lai=2
// value_size=4: float→warps=4,ipt=88-1,lai=3; int→warps=4,ipt=80-1,lai=3
// value_size=8: warps=2, ipt=88-1, lai=5
// value_size=16: warps=5, ipt=16-1, lai=8
// Helper: construct mem-scaled lookback policy (mirrors CCCL make_mem_scaled_lookback_scan_policy)
// ============================================================
// --- Lookback tunings for BI-V100 ---
constexpr ScanPolicy make_lookback_policy(
int nominal_threads,
int nominal_items,
int compute_t_size,
BlockLoadAlgorithm load_algo,
CacheLoadModifier load_mod,
BlockStoreAlgorithm store_algo,
BlockScanAlgorithm scan_algo,
LookbackDelayPolicy delay = {LookbackDelayAlgorithm::fixed_delay, 350, 450})
{
auto [items, threads] = scale_mem_bound(nominal_threads, nominal_items, compute_t_size);
return ScanPolicy{
ScanAlgorithm::lookback,
ScanLookbackPolicy{threads, items, load_algo, load_mod, store_algo, scan_algo, delay},
ScanLookaheadPolicy{}
};
}
// ============================================================
// BI-V100 tuning tables
//
// Derived from CCCL SM100 benchmark data with BI-V100 adaptations:
// - SMEM cap: tile = tpb × ipt × value_size ≤ 49152
// - delay_ns scaled ×0.5 (fewer concurrent tiles on 16 SMs)
// - l2_write_latency scaled ×0.6 (6MB L2 vs 64MB)
// - All use lookback (no lookahead — PTX ISA not available)
//
// Nomenclature:
// bi100_lookback_{value_size}B_o{offset_size}
// value_size = sizeof(InputValueT), offset_size = sizeof(OffsetT)
// ============================================================
// --- plus<> operator, offset_size=4 ---
// CCCL SM100: ipt_18.tpb_512.ns_768.dcid_7.l2w_820.trp_1.ld_0 1.189 1.006 1.173 1.305
// value_size=1: tile = 512×18×1 = 9216 ≤ 49152 ✓
// BI-V100: 16 SMs → increase items for fewer CTAs (more work per CTA)
struct bi100_lookback_1B_o4 {
// SM100 ref: ipt_18.tpb_512.ns_768.dcid_7.l2w_820 → 1.189x
// SM=16 fix: tile = 512*18*1 = 9216 (19% SMEM — too small for 16 SMs)
// Increase items: 512*32*1 = 16384 (33% SMEM, scan needs input+output buffer)
// scan_tile = threads * items * accum_size * 2 (input+output) for SMEM
// 512 * 32 * 1 * 2 = 32768 (67% SMEM) — good balance
static constexpr int threads = 512;
static constexpr int items = 32;
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::no_delay, 0, 492};
static constexpr int items = 32; // raised from 18: tile=16384, still <<49152
static constexpr BlockLoadAlgorithm load_algo = BLOCK_LOAD_WARP_TRANSPOSE;
static constexpr BlockStoreAlgorithm store_algo = BLOCK_STORE_WARP_TRANSPOSE;
static constexpr CacheLoadModifier load_mod = LOAD_DEFAULT;
static constexpr BlockStoreAlgorithm store_algo = BLOCK_STORE_WARP_TRANSPOSE;
// dcid_7=exponential_backon, ns=768×0.5=384, l2w=820×0.6=492
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::exponential_backon, 384, 492};
};
// CCCL SM100: ipt_13.tpb_512.ns_1384.dcid_7.l2w_720.trp_1.ld_0 1.128 1.003 1.120 1.308
// value_size=2: tile = 512×13×2 = 13312 ≤ 49152 ✓
struct bi100_lookback_2B_o4 {
// SM100 ref: ipt_13.tpb_512.ns_1384.dcid_7.l2w_720 → 1.128x
// SM=16 fix: tile = 512*13*2 = 13312 (27% SMEM)
// Increase: 512*24*2 = 24576 → scan buffer = 24576*2 = 49152 (100% SMEM)
static constexpr int threads = 512;
static constexpr int items = 24;
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::no_delay, 0, 432};
static constexpr int items = 22; // raised from 13: tile=22528 ≤ 49152 ✓
static constexpr BlockLoadAlgorithm load_algo = BLOCK_LOAD_WARP_TRANSPOSE;
static constexpr BlockStoreAlgorithm store_algo = BLOCK_STORE_WARP_TRANSPOSE;
static constexpr CacheLoadModifier load_mod = LOAD_DEFAULT;
static constexpr BlockStoreAlgorithm store_algo = BLOCK_STORE_WARP_TRANSPOSE;
// dcid_7=exponential_backon, ns=1384×0.5=692, l2w=720×0.6=432
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::exponential_backon, 692, 432};
};
// CCCL SM100: ipt_22.tpb_384.ns_1904.dcid_6.l2w_830.trp_1.ld_0 1.148 0.997 1.140 1.463
// value_size=4 (float32 — HOT PATH: paged_attention softmax denominator):
// SM100 tile = 384×22×4 = 33792 ≤ 49152 ✓
// BI-V100: keep items=22 (already near SMEM-optimal tile size for 48KB)
struct bi100_lookback_4B_o4 {
// BI-V100 BENCHMARK RESULT (bench_bi100.py scan/float32):
// #1: dcid_0.ipt_22.l2w_500.ld_0.ns_1904.tpb_384.trp_1
// speedups: 1.038085 1.009473 1.007679 1.005803 SMEM=33792 (69%)
//
// KEY FINDING: ns=1904 (same as SM100 raw, NOT ×0.5!)
// The ns×0.5 heuristic was WRONG for BI-V100.
// dcid=0 (no_delay) beat dcid=6 (exponential_backon_jitter).
// With only 16 SMs → ~32 concurrent CTAs → minimal lookback contention
// → simple no_delay with ns=1904 spacing is optimal.
static constexpr int threads = 384;
static constexpr int items = 22;
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::no_delay, 1904, 500};
static constexpr int items = 22; // same as SM100 — already optimal tile ratio
static constexpr BlockLoadAlgorithm load_algo = BLOCK_LOAD_WARP_TRANSPOSE;
static constexpr BlockStoreAlgorithm store_algo = BLOCK_STORE_WARP_TRANSPOSE;
static constexpr CacheLoadModifier load_mod = LOAD_DEFAULT;
};
struct bi100_lookback_4B_o8 {
// SM100 ref: ipt_19.tpb_416.ns_956.dcid_7.l2w_550 → 1.146x
static constexpr int threads = 416;
static constexpr int items = 19;
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::no_delay, 0, 330};
static constexpr BlockLoadAlgorithm load_algo = BLOCK_LOAD_WARP_TRANSPOSE;
static constexpr BlockStoreAlgorithm store_algo = BLOCK_STORE_WARP_TRANSPOSE;
static constexpr CacheLoadModifier load_mod = LOAD_CA;
// dcid_6=exponential_backon_jitter, ns=1904×0.5=952, l2w=830×0.6=498
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::exponential_backon_jitter, 952, 498};
};
// CCCL SM100: ipt_23.tpb_416.ns_772.dcid_5.l2w_710.trp_1.ld_0 1.089 1.016 1.086 1.265
// value_size=8 (int64/double):
// SM100 tile = 416×23×8 = 76544 > 49152 OVERFLOW!
// BI-V100 max_items = floor(49152 / (416×8)) = 14
// But with threads=320: floor(49152 / (320×8)) = 19
struct bi100_lookback_8B_o4 {
// SM100 ref: ipt_23.tpb_416 → tile=76544 > 49152 SMEM OVERFLOW!
// Fix: items = floor(49152/(384*8)) = 16 → tile = 384*16*8 = 49152 (100%)
// Changed threads 416→384 (multiple of 32) for cleaner warp alignment
static constexpr int threads = 384;
static constexpr int items = 16;
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::no_delay, 0, 426};
static constexpr BlockLoadAlgorithm load_algo = BLOCK_LOAD_WARP_TRANSPOSE;
static constexpr BlockStoreAlgorithm store_algo = BLOCK_STORE_WARP_TRANSPOSE;
static constexpr CacheLoadModifier load_mod = LOAD_DEFAULT;
};
struct bi100_lookback_8B_o8 {
// SM100 ref: ipt_22.tpb_320 → tile=56320 > 49152 SMEM OVERFLOW!
// Fix: items = floor(49152/(320*8)) = 19 → tile = 320*19*8 = 48640 (99%)
// 19 items confirmed safe, maximizes SMEM within constraint
static constexpr int threads = 320;
static constexpr int items = 19;
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::no_delay, 0, 579};
static constexpr int items = 19; // SMEM capped: 320×19×8 = 48640 ≤ 49152 ✓ (99% utilization!)
static constexpr BlockLoadAlgorithm load_algo = BLOCK_LOAD_WARP_TRANSPOSE;
static constexpr BlockStoreAlgorithm store_algo = BLOCK_STORE_WARP_TRANSPOSE;
static constexpr CacheLoadModifier load_mod = LOAD_DEFAULT;
static constexpr BlockStoreAlgorithm store_algo = BLOCK_STORE_WARP_TRANSPOSE;
// dcid_5=exponential_backon_jitter_window, ns=772×0.5=386, l2w=710×0.6=426
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::exponential_backon_jitter_window, 386, 426};
};
// --- plus<> operator, offset_size=8 ---
// CCCL SM100: ipt_14.tpb_384.ns_228.dcid_7.l2w_775.trp_1.ld_1 1.107 1.000 1.101 1.308
// value_size=1, offset=8: tile = 384×14×1 = 5376 ≤ 49152 ✓
struct bi100_lookback_1B_o8 {
// CCCL SM100 ref: ipt_14.tpb_384.ns_228.dcid_7.l2w_775 → 1.107x
// BI-V100 derived: delay halved (L2 6MB vs 50MB), LOAD_CA matches SM100
// nominal_tile = 384*14*4 = 21504 ≤ 49152 ✓
static constexpr int threads = 384;
static constexpr int items = 14;
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::no_delay, 0, 465};
static constexpr int items = 28; // raised from 14: tile=10752, BI-V100 wants larger tiles
static constexpr BlockLoadAlgorithm load_algo = BLOCK_LOAD_WARP_TRANSPOSE;
static constexpr CacheLoadModifier load_mod = LOAD_DEFAULT; // SM100 used LOAD_CA(ld_1), but BI-V100 prefers DEFAULT
static constexpr BlockStoreAlgorithm store_algo = BLOCK_STORE_WARP_TRANSPOSE;
static constexpr CacheLoadModifier load_mod = LOAD_CA;
};
// --- Lookahead tunings for BI-V100 ---
struct bi100_lookahead_1B {
// SM100 ref: wrps_4.lbi_8.ipt_160 → 1.264x
static constexpr int warps = 4;
static constexpr int items = 159; // 160-1
static constexpr int lookahead_items = 8;
};
struct bi100_lookahead_2B {
// SM100 ref: wrps_6.lbi_2.ipt_96 → 1.168x
static constexpr int warps = 6;
static constexpr int items = 95; // 96-1
static constexpr int lookahead_items = 2;
};
struct bi100_lookahead_4B {
// SM100 ref (int): wrps_4.lbi_3.ipt_80 → 1.019x
static constexpr int warps = 4;
static constexpr int items = 79; // 80-1
static constexpr int lookahead_items = 3;
};
struct bi100_lookahead_4B_float {
// SM100 ref (float32): wrps_4.lbi_3.ipt_88 → 1.047x
static constexpr int warps = 4;
static constexpr int items = 87; // 88-1
static constexpr int lookahead_items = 3;
};
struct bi100_lookahead_8B {
// SM100 ref: wrps_2.lbi_5.ipt_88 → 1.086x
static constexpr int warps = 2;
static constexpr int items = 87; // 88-1
static constexpr int lookahead_items = 5;
};
struct bi100_lookahead_16B {
// SM100 ref: wrps_5.lbi_8.ipt_16 → 1.160x
static constexpr int warps = 5;
static constexpr int items = 15; // 16-1
static constexpr int lookahead_items = 8;
};
// --- Lookback default fallback ---
struct bi100_lookback_default {
static constexpr int threads = 128;
static constexpr int items = 15;
// dcid_7=exponential_backon, ns=228×0.5=114, l2w=775×0.6=465
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::no_delay, 0, 450};
LookbackDelayAlgorithm::exponential_backon, 114, 465};
};
// CCCL SM100: no specialization for value_size=2, offset=8 (regresses for large inputs)
// Fall through to SM90 tuning
// CCCL SM100: ipt_19.tpb_416.ns_956.dcid_7.l2w_550.trp_1.ld_1 1.146 0.994 1.137 1.456
// value_size=4, offset=8: tile = 416×19×4 = 31616 ≤ 49152 ✓
struct bi100_lookback_4B_o8 {
static constexpr int threads = 416;
static constexpr int items = 19; // same as SM100
static constexpr BlockLoadAlgorithm load_algo = BLOCK_LOAD_WARP_TRANSPOSE;
static constexpr CacheLoadModifier load_mod = LOAD_DEFAULT; // SM100 used LOAD_CA
static constexpr BlockStoreAlgorithm store_algo = BLOCK_STORE_WARP_TRANSPOSE;
// dcid_7=exponential_backon, ns=956×0.5=478, l2w=550×0.6=330
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::exponential_backon, 478, 330};
};
// CCCL SM100: ipt_22.tpb_320.ns_328.dcid_2.l2w_965.trp_1.ld_0 1.080 1.000 1.076 1.249
// value_size=8, offset=8: tile = 320×22×8 = 56320 > 49152 OVERFLOW!
// BI-V100 max_items = floor(49152 / (320×8)) = 19
struct bi100_lookback_8B_o8 {
static constexpr int threads = 320;
static constexpr int items = 19; // SMEM capped: 320×19×8 = 48640 ≤ 49152 ✓
static constexpr BlockLoadAlgorithm load_algo = BLOCK_LOAD_WARP_TRANSPOSE;
static constexpr CacheLoadModifier load_mod = LOAD_DEFAULT;
static constexpr BlockStoreAlgorithm store_algo = BLOCK_STORE_WARP_TRANSPOSE;
// dcid_2=exponential_backoff, ns=328×0.5=164, l2w=965×0.6=579
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::exponential_backoff, 164, 579};
};
// --- SM90 fallback tunings (used when SM100 has no specialization) ---
// These come from CCCL sm90_tuning tables, with SMEM-capped items for BI-V100.
// All use fixed_delay (SM90 didn't have the advanced delay algorithms).
//
// CCCL SM90 table (fixed_delay_constructor_t<ns, l2w>):
// accum_size=1: tpb=192, ipt=22, ns=168, l2w=1140
// accum_size=2: tpb=512, ipt=12, ns=376, l2w=1125
// accum_size=4: tpb=128, ipt=24, ns=648, l2w=1245 (generic)
// float32: tpb=128, ipt=24, ns=688, l2w=1140
// accum_size=8: tpb=224, ipt=24, ns=632, l2w=1290 (generic)
// float64: tpb=224, ipt=24, ns=576, l2w=1215
// accum_size=16(int128): tpb=576, ipt=21, ns=860, l2w=630
struct bi100_sm90_accum1 {
static constexpr int threads = 192;
static constexpr int items = 32; // raised from 22: tile=6144 (accum=1B), <<49152
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 84, 684}; // ns×0.5, l2w×0.6
};
struct bi100_sm90_accum2 {
static constexpr int threads = 512;
static constexpr int items = 22; // raised from 12: tile=22528 (accum=2B), ≤49152 ✓
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 188, 675};
};
struct bi100_sm90_accum4_generic {
static constexpr int threads = 128;
static constexpr int items = 24; // same as SM90: tile=12288 (accum=4B), ≤49152 ✓
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 324, 747};
};
struct bi100_sm90_float32 {
static constexpr int threads = 128;
static constexpr int items = 24; // same as SM90: tile=12288, ≤49152 ✓
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 344, 684};
};
struct bi100_sm90_accum8_generic {
static constexpr int threads = 224;
static constexpr int items = 24; // SM90: tile=224×24×8=43008, ≤49152 ✓ (87% utilization)
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 316, 774};
};
struct bi100_sm90_float64 {
static constexpr int threads = 224;
static constexpr int items = 24; // same as SM90: tile=43008, ≤49152 ✓
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 288, 729};
};
struct bi100_sm90_accum16 {
// SM90: tpb=576, ipt=21 → tile=576×21×16=193536 OVERFLOW!
// BI-V100: max_items = floor(49152/(192×16))=16, or floor(49152/(128×16))=24
static constexpr int threads = 192;
static constexpr int items = 16; // SMEM capped: 192×16×16 = 49152 = EXACT FIT
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 430, 378};
};
// --- SM80 fallback tunings (for non-plus operators or non-primitive accumulators) ---
// CCCL SM80 table:
// accum_size=1: tpb=320, ipt=14, ns=368, l2w=725
// accum_size=2: tpb=352, ipt=16, ns=488, l2w=1040
// accum_size=4: tpb=320, ipt=12, ns=268, l2w=1180 (generic)
// float32: tpb=288, ipt=8, ns=724, l2w=1050
// accum_size=8: tpb=288, ipt=22, ns=716, l2w=785 (generic)
// float64: tpb=384, ipt=12, ns=388, l2w=1100
// int128: tpb=640, ipt=24, ns=1200, l2w=0 (BLOCK_LOAD_DIRECT)
struct bi100_sm80_accum1 {
static constexpr int threads = 320;
static constexpr int items = 28; // raised from 14: tile=8960 (1B), <<49152
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 184, 435};
};
struct bi100_sm80_accum2 {
static constexpr int threads = 352;
static constexpr int items = 24; // raised from 16: tile=16896 (2B), ≤49152 ✓
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 244, 624};
};
struct bi100_sm80_accum4_generic {
static constexpr int threads = 320;
static constexpr int items = 24; // raised from 12: tile=30720 (4B), ≤49152 ✓
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 134, 708};
};
struct bi100_sm80_float32 {
static constexpr int threads = 288;
static constexpr int items = 24; // raised from 8: tile=27648 (4B), ≤49152 ✓
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 362, 630};
};
struct bi100_sm80_accum8_generic {
static constexpr int threads = 288;
static constexpr int items = 20; // SMEM limited: 288×22×8=50688>49152, use 20→46080 ✓
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 358, 471};
};
struct bi100_sm80_float64 {
static constexpr int threads = 384;
static constexpr int items = 16; // SMEM limited: 384×12×8=36864 → can raise to 16→49152 EXACT FIT
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 194, 660};
};
struct bi100_sm80_int128 {
// SM80: tpb=640, ipt=24, BLOCK_LOAD_DIRECT → no SMEM staging for load
// But BLOCK_STORE_DIRECT also avoids SMEM → register-only pipeline
// BI-V100: safe at 640×24 since direct load doesn't use SMEM for staging
static constexpr int threads = 640;
static constexpr int items = 16; // conservative: 640×16×16=163840 regs only (no SMEM staging)
static constexpr BlockLoadAlgorithm load_algo = BLOCK_LOAD_DIRECT;
static constexpr CacheLoadModifier load_mod = LOAD_DEFAULT;
static constexpr BlockStoreAlgorithm store_algo = BLOCK_STORE_DIRECT;
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::no_delay, 0, 600};
};
// --- Default fallback (for non-tuned types/operators) ---
// CCCL: tpb=128, ipt=15 with default delay
struct bi100_default {
static constexpr int threads = 128;
static constexpr int items = 24; // raised from 15: 128×24×4=12288 ≤ 49152 for 4B types
static constexpr LookbackDelayPolicy delay = {
LookbackDelayAlgorithm::fixed_delay, 350, 450};
};
// ============================================================
// policy_selector
//
// Mirrors CCCL's policy_selector with the same field signature.
// BI-V100 ALWAYS returns ScanAlgorithm::lookback (no lookahead).
//
// Dispatch priority:
// 1. SM100 benchmark-matched tunings (plus + primitive + matching value/offset sizes)
// 2. SM90 accum-size tunings (plus + primitive accum)
// 3. SM80 accum-size tunings (primitive op + primitive accum)
// 4. Default fallback
// ============================================================
struct policy_selector {
int input_value_size;
int input_value_alignment;
int output_value_size;
int output_value_alignment;
int accum_size;
int accum_alignment;
int offset_size;
type_t input_type;
type_t accum_type;
op_kind_t operation_t;
bool is_primitive_accum;
bool input_contiguous;
bool output_contiguous;
bool input_trivially_copyable;
bool output_trivially_copyable;
bool output_default_constructible;
bool accum_is_primitive_or_trivially_copy_constructible;
bool benchmark_match;
bool require_stable_reduction_order = false;
constexpr ScanPolicy operator()(const hardware_capability& hw) const {
// BI-V100: always lookback (no lookahead — PTX ISA too old)
const bool large_values = accum_size > 128;
const BlockLoadAlgorithm transposed_load =
large_values ? BLOCK_LOAD_WARP_TRANSPOSE_TIMESLICED : BLOCK_LOAD_WARP_TRANSPOSE;
const BlockStoreAlgorithm transposed_store =
large_values ? BLOCK_STORE_WARP_TRANSPOSE_TIMESLICED : BLOCK_STORE_WARP_TRANSPOSE;
if (!hw.at_least(hardware_capability::vendor_t::iluvatar, 100)) {
// Non BI-V100: fall through to default
return make_lookback_policy(
bi100_default::threads, bi100_default::items, accum_size,
transposed_load, LOAD_DEFAULT, transposed_store,
BLOCK_SCAN_WARP_SCANS, bi100_default::delay);
}
// ---- Tier 1: SM100 benchmark-matched (highest priority) ----
// Only for plus<> + primitive accum + benchmark_match
if (benchmark_match && operation_t == op_kind_t::plus
&& accum_is_primitive_or_trivially_copy_constructible) {
/// Get the best lookback policy for BI-V100
constexpr ScanLookbackPolicy get_lookback(const hardware_capability& hw) const {
if (hw.at_least(hardware_capability::vendor_t::iluvatar, 100)
&& operation_t == op_kind_t::plus && is_primitive_accum) {
if (offset_size == 4) {
switch (input_value_size) {
case 1: return {bi100_lookback_1B_o4::threads, bi100_lookback_1B_o4::items,
bi100_lookback_1B_o4::load_algo, bi100_lookback_1B_o4::load_mod,
bi100_lookback_1B_o4::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_1B_o4::delay};
case 2: return {bi100_lookback_2B_o4::threads, bi100_lookback_2B_o4::items,
bi100_lookback_2B_o4::load_algo, bi100_lookback_2B_o4::load_mod,
bi100_lookback_2B_o4::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_2B_o4::delay};
case 4: return {bi100_lookback_4B_o4::threads, bi100_lookback_4B_o4::items,
bi100_lookback_4B_o4::load_algo, bi100_lookback_4B_o4::load_mod,
bi100_lookback_4B_o4::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_4B_o4::delay};
case 8: return {bi100_lookback_8B_o4::threads, bi100_lookback_8B_o4::items,
bi100_lookback_8B_o4::load_algo, bi100_lookback_8B_o4::load_mod,
bi100_lookback_8B_o4::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_8B_o4::delay};
case 1:
return make_lookback_policy(
bi100_lookback_1B_o4::threads, bi100_lookback_1B_o4::items, accum_size,
bi100_lookback_1B_o4::load_algo, bi100_lookback_1B_o4::load_mod,
bi100_lookback_1B_o4::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_1B_o4::delay);
case 2:
return make_lookback_policy(
bi100_lookback_2B_o4::threads, bi100_lookback_2B_o4::items, accum_size,
bi100_lookback_2B_o4::load_algo, bi100_lookback_2B_o4::load_mod,
bi100_lookback_2B_o4::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_2B_o4::delay);
case 4:
return make_lookback_policy(
bi100_lookback_4B_o4::threads, bi100_lookback_4B_o4::items, accum_size,
bi100_lookback_4B_o4::load_algo, bi100_lookback_4B_o4::load_mod,
bi100_lookback_4B_o4::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_4B_o4::delay);
case 8:
return make_lookback_policy(
bi100_lookback_8B_o4::threads, bi100_lookback_8B_o4::items, accum_size,
bi100_lookback_8B_o4::load_algo, bi100_lookback_8B_o4::load_mod,
bi100_lookback_8B_o4::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_8B_o4::delay);
default: break;
}
} else if (offset_size == 8) {
}
else if (offset_size == 8) {
switch (input_value_size) {
case 1: return {bi100_lookback_1B_o8::threads, bi100_lookback_1B_o8::items,
bi100_lookback_1B_o8::load_algo, bi100_lookback_1B_o8::load_mod,
bi100_lookback_1B_o8::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_1B_o8::delay};
case 4: return {bi100_lookback_4B_o8::threads, bi100_lookback_4B_o8::items,
bi100_lookback_4B_o8::load_algo, bi100_lookback_4B_o8::load_mod,
bi100_lookback_4B_o8::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_4B_o8::delay};
case 8: return {bi100_lookback_8B_o8::threads, bi100_lookback_8B_o8::items,
bi100_lookback_8B_o8::load_algo, bi100_lookback_8B_o8::load_mod,
bi100_lookback_8B_o8::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_8B_o8::delay};
case 1:
return make_lookback_policy(
bi100_lookback_1B_o8::threads, bi100_lookback_1B_o8::items, accum_size,
bi100_lookback_1B_o8::load_algo, bi100_lookback_1B_o8::load_mod,
bi100_lookback_1B_o8::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_1B_o8::delay);
// case 2: intentionally omitted — CCCL SM100 also omits (regresses for large inputs)
case 4:
return make_lookback_policy(
bi100_lookback_4B_o8::threads, bi100_lookback_4B_o8::items, accum_size,
bi100_lookback_4B_o8::load_algo, bi100_lookback_4B_o8::load_mod,
bi100_lookback_4B_o8::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_4B_o8::delay);
case 8:
if (accum_type == type_t::float64) {
break; // float64 + offset=8: CCCL falls through to SM90 too
}
return make_lookback_policy(
bi100_lookback_8B_o8::threads, bi100_lookback_8B_o8::items, accum_size,
bi100_lookback_8B_o8::load_algo, bi100_lookback_8B_o8::load_mod,
bi100_lookback_8B_o8::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_8B_o8::delay);
default: break;
}
}
}
// Fallback
return {bi100_lookback_default::threads, bi100_lookback_default::items,
bi100_lookback_default::load_algo, bi100_lookback_default::load_mod,
bi100_lookback_default::store_algo, BLOCK_SCAN_WARP_SCANS,
bi100_lookback_default::delay};
}
// ---- Tier 2: SM90-level accum-size tunings ----
// For plus<> + primitive accum, dispatch by accum_size
if (operation_t != op_kind_t::other
&& accum_is_primitive_or_trivially_copy_constructible) {
/// Get the best lookahead policy for BI-V100
constexpr ScanLookaheadPolicy get_lookahead(const hardware_capability& hw) const {
// Lookahead requires specific hardware features (pipeline stages, etc.)
// BI-V100 support is TBD — if not available, caller falls back to lookback
if (!hw.at_least(hardware_capability::vendor_t::iluvatar, 100))
return {4, 63, 4, 2, -1}; // conservative default
if (is_primitive_accum) {
switch (input_value_size) {
case 1: return {bi100_lookahead_1B::warps, bi100_lookahead_1B::items,
bi100_lookahead_1B::lookahead_items, 2, -1};
case 2: return {bi100_lookahead_2B::warps, bi100_lookahead_2B::items,
bi100_lookahead_2B::lookahead_items, 2, -1};
switch (accum_size) {
case 1:
return make_lookback_policy(
bi100_sm90_accum1::threads, bi100_sm90_accum1::items, accum_size,
BLOCK_LOAD_WARP_TRANSPOSE, LOAD_DEFAULT, BLOCK_STORE_WARP_TRANSPOSE,
BLOCK_SCAN_WARP_SCANS, bi100_sm90_accum1::delay);
case 2:
return make_lookback_policy(
bi100_sm90_accum2::threads, bi100_sm90_accum2::items, accum_size,
BLOCK_LOAD_WARP_TRANSPOSE, LOAD_DEFAULT, BLOCK_STORE_WARP_TRANSPOSE,
BLOCK_SCAN_WARP_SCANS, bi100_sm90_accum2::delay);
case 4:
if (input_type == type_t::float32)
return {bi100_lookahead_4B_float::warps, bi100_lookahead_4B_float::items,
bi100_lookahead_4B_float::lookahead_items, 2, -1};
return {bi100_lookahead_4B::warps, bi100_lookahead_4B::items,
bi100_lookahead_4B::lookahead_items, 2, -1};
case 8: return {bi100_lookahead_8B::warps, bi100_lookahead_8B::items,
bi100_lookahead_8B::lookahead_items, 2, -1};
case 16: return {bi100_lookahead_16B::warps, bi100_lookahead_16B::items,
bi100_lookahead_16B::lookahead_items, 2, -1};
if (accum_type == type_t::float32) {
return make_lookback_policy(
bi100_sm90_float32::threads, bi100_sm90_float32::items, accum_size,
BLOCK_LOAD_WARP_TRANSPOSE, LOAD_DEFAULT, BLOCK_STORE_WARP_TRANSPOSE,
BLOCK_SCAN_WARP_SCANS, bi100_sm90_float32::delay);
}
return make_lookback_policy(
bi100_sm90_accum4_generic::threads, bi100_sm90_accum4_generic::items, accum_size,
BLOCK_LOAD_WARP_TRANSPOSE, LOAD_DEFAULT, BLOCK_STORE_WARP_TRANSPOSE,
BLOCK_SCAN_WARP_SCANS, bi100_sm90_accum4_generic::delay);
case 8:
if (accum_type == type_t::float64) {
return make_lookback_policy(
bi100_sm90_float64::threads, bi100_sm90_float64::items, accum_size,
BLOCK_LOAD_WARP_TRANSPOSE, LOAD_DEFAULT, BLOCK_STORE_WARP_TRANSPOSE,
BLOCK_SCAN_WARP_SCANS, bi100_sm90_float64::delay);
}
return make_lookback_policy(
bi100_sm90_accum8_generic::threads, bi100_sm90_accum8_generic::items, accum_size,
BLOCK_LOAD_WARP_TRANSPOSE, LOAD_DEFAULT, BLOCK_STORE_WARP_TRANSPOSE,
BLOCK_SCAN_WARP_SCANS, bi100_sm90_accum8_generic::delay);
case 16:
if (accum_type == type_t::int128 || accum_type == type_t::uint128) {
return make_lookback_policy(
bi100_sm90_accum16::threads, bi100_sm90_accum16::items, accum_size,
BLOCK_LOAD_WARP_TRANSPOSE, LOAD_DEFAULT, BLOCK_STORE_WARP_TRANSPOSE,
BLOCK_SCAN_WARP_SCANS, bi100_sm90_accum16::delay);
}
break;
default: break;
}
}
// Fallback lookahead
int default_items = (256 / (input_value_size == 2 ? 2 : accum_size)) - 1;
if (default_items < 1) default_items = 1;
int lai = accum_size == 2 ? 3 : 4;
return {4, default_items, lai, 2, -1};
}
// ---- Tier 3: SM80-level tunings ----
// For primitive op + primitive accum
if (operation_t != op_kind_t::other) {
if (accum_is_primitive_or_trivially_copy_constructible) {
switch (accum_size) {
case 1:
return make_lookback_policy(
bi100_sm80_accum1::threads, bi100_sm80_accum1::items, accum_size,
BLOCK_LOAD_WARP_TRANSPOSE, LOAD_DEFAULT, BLOCK_STORE_WARP_TRANSPOSE,
BLOCK_SCAN_WARP_SCANS, bi100_sm80_accum1::delay);
case 2:
return make_lookback_policy(
bi100_sm80_accum2::threads, bi100_sm80_accum2::items, accum_size,
BLOCK_LOAD_WARP_TRANSPOSE, LOAD_DEFAULT, BLOCK_STORE_WARP_TRANSPOSE,
BLOCK_SCAN_WARP_SCANS, bi100_sm80_accum2::delay);
case 4:
if (accum_type == type_t::float32) {
return make_lookback_policy(
bi100_sm80_float32::threads, bi100_sm80_float32::items, accum_size,
BLOCK_LOAD_WARP_TRANSPOSE, LOAD_DEFAULT, BLOCK_STORE_WARP_TRANSPOSE,
BLOCK_SCAN_WARP_SCANS, bi100_sm80_float32::delay);
}
return make_lookback_policy(
bi100_sm80_accum4_generic::threads, bi100_sm80_accum4_generic::items, accum_size,
BLOCK_LOAD_WARP_TRANSPOSE, LOAD_DEFAULT, BLOCK_STORE_WARP_TRANSPOSE,
BLOCK_SCAN_WARP_SCANS, bi100_sm80_accum4_generic::delay);
case 8:
if (accum_type == type_t::float64) {
return make_lookback_policy(
bi100_sm80_float64::threads, bi100_sm80_float64::items, accum_size,
BLOCK_LOAD_WARP_TRANSPOSE, LOAD_DEFAULT, BLOCK_STORE_WARP_TRANSPOSE,
BLOCK_SCAN_WARP_SCANS, bi100_sm80_float64::delay);
}
return make_lookback_policy(
bi100_sm80_accum8_generic::threads, bi100_sm80_accum8_generic::items, accum_size,
BLOCK_LOAD_WARP_TRANSPOSE, LOAD_DEFAULT, BLOCK_STORE_WARP_TRANSPOSE,
BLOCK_SCAN_WARP_SCANS, bi100_sm80_accum8_generic::delay);
case 16:
// int128 with BLOCK_LOAD_DIRECT (no SMEM staging)
return make_lookback_policy(
bi100_sm80_int128::threads, bi100_sm80_int128::items, accum_size,
bi100_sm80_int128::load_algo, bi100_sm80_int128::load_mod,
bi100_sm80_int128::store_algo,
BLOCK_SCAN_WARP_SCANS, bi100_sm80_int128::delay);
default: break;
}
}
}
/// Main dispatch — matches CCCL's operator()(cuda::compute_capability)
constexpr ScanPolicy operator()(const hardware_capability& hw) const {
// Try lookahead first (if hardware supports it)
// TODO: add can_use_lookahead check once BI-V100 pipeline support is confirmed
auto lookahead = get_lookahead(hw);
// For now, default to lookback (safer, works on all hardware)
auto lookback = get_lookback(hw);
return {ScanAlgorithm::lookback, lookback, lookahead};
// ---- Tier 4: Default fallback ----
return make_lookback_policy(
bi100_default::threads, bi100_default::items, accum_size,
transposed_load, LOAD_DEFAULT, transposed_store,
BLOCK_SCAN_WARP_SCANS, bi100_default::delay);
}
};