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FA3 tensor size parameter fix for long context len (seqlen >=4M) #1841

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Merged
tridao merged 1 commit into from
Aug 26, 2025
Merged

FA3 tensor size parameter fix for long context len (seqlen >=4M) #1841

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8 changes: 4 additions & 4 deletions hopper/tile_scheduler.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -251,7 +251,7 @@ class DynamicPersistentTileScheduler {

static Params
to_underlying_arguments(TileSchedulerArguments const& args) {
int const size_one_kv_head = args.seqlen_k * (args.headdim + args.headdim_v) * args.element_size;
long long const size_one_kv_head = long(args.seqlen_k) * long(args.headdim + args.headdim_v) * long(args.element_size);
int const size_l2 = 32 * 1024 * 1024; // 32 MB for K & V
// Swizzle is the size of each "section". Round swizzle to a power of 2
// If not PackGQA already, the size of each section can increase by qhead_per_khead
Expand Down Expand Up @@ -382,9 +382,9 @@ class SingleTileBwdLPTScheduler {
static Params
to_underlying_arguments(TileSchedulerArguments const& args) {
// Since it's the bwd pass, seqlen_k get passed to args.seqlen and seqlen_q is passed to args.seqlen_k
int const size_one_qdo_head = args.seqlen_k * (args.headdim + args.headdim_v) * args.element_size;
int const size_one_dqaccum_head = args.seqlen_k * args.headdim * sizeof(float);
int const size_one_head = size_one_qdo_head + size_one_dqaccum_head;
long long const size_one_qdo_head = long(args.seqlen_k) * long(args.headdim + args.headdim_v) * long(args.element_size);
long long const size_one_dqaccum_head = long(args.seqlen_k) * long(args.headdim) * sizeof(float);
long long const size_one_head = size_one_qdo_head + size_one_dqaccum_head;
int const size_l2 = 40 * 1024 * 1024; // 40 MB for Q, dO, and dQaccum
// Swizzle is the size of each "section". Round swizzle to a power of 2
// Need to be careful about the case where only one head will fit
Expand Down