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metal : skip loading all-zero mask #19337

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Merged
ggerganov merged 2 commits into from
Feb 6, 2026
+39 −24
Merged

metal : skip loading all-zero mask #19337

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4815a66
metal : skip loading all-zero mask
ggerganov Feb 4, 2026
fd56915
cont : minor
ggerganov Feb 5, 2026
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63 changes: 39 additions & 24 deletions ggml/src/ggml-metal/ggml-metal.metal
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Original file line number Diff line number Diff line change
Expand Up @@ -5285,6 +5285,7 @@ constant int32_t FC_flash_attn_ext_blk_ncpsg [[function_constant(FC_FLASH_ATTN_E
// scan the blocks of the mask that are not masked
// 0 - masked (i.e. full of -INF, skip)
// 1 - not masked (i.e. at least one element of the mask is not -INF)
// 2 - all zero
kernel void kernel_flash_attn_ext_blk(
constant ggml_metal_kargs_flash_attn_ext_blk & args,
device const char * mask,
Expand All @@ -5306,27 +5307,29 @@ kernel void kernel_flash_attn_ext_blk(

device const half * mask_src = (device const half *) (mask + (i1*Q)*args.nb31 + i2*args.nb32 + i3*args.nb33) + i0*C + tiisg;

// fast route
if (res == 0) {
if (simd_max(*mask_src) > -MAXHALF/2) {
res = 1;
}
}

// detailed check of the elements of the block
if ((C > NW || Q > 1) && res == 0) {
half m = -MAXHALF;
half mmin = MAXHALF;
half mmax = -MAXHALF;

FOR_UNROLL (short j = 0; j < Q; ++j) {
FOR_UNROLL (short ii = 0; ii < C/NW; ++ii) {
m = max(m, mask_src[ii*NW]);
mmin = min(mmin, mask_src[ii*NW]);
mmax = max(mmax, mask_src[ii*NW]);
}

mask_src += args.nb31/2;
}

if (simd_max(m) > -MAXHALF/2) {
res = 1;
mmin = simd_min(mmin);
mmax = simd_max(mmax);

if (mmax > -MAXHALF) {
if (mmin == 0.0 && mmax == 0.0) {
res = 2;
} else {
res = 1;
}
}
}

Expand Down Expand Up @@ -5568,26 +5571,36 @@ void kernel_flash_attn_ext_impl(
ic = 0;
}

char blk_cur = 1;

// read the mask into shared mem
if (FC_flash_attn_ext_has_mask) {
if (blk[ic0] == 0) {
blk_cur = blk[ic0];

if (blk_cur == 0) {
FOR_UNROLL (short jj = 0; jj < NQ; ++jj) {
pm2[jj] += NW;
}

continue;
}

FOR_UNROLL (short jj = 0; jj < NQ; ++jj) {
const short j = jj*NSG + sgitg;
if (blk_cur == 1) {
FOR_UNROLL (short jj = 0; jj < NQ; ++jj) {
const short j = jj*NSG + sgitg;

if (FC_flash_attn_ext_bc_mask) {
sm2[j*SH + tiisg] = (iq1 + j) < args.ne31 ? pm2[jj][tiisg] : half2(-MAXHALF, -MAXHALF);
} else {
sm2[j*SH + tiisg] = pm2[jj][tiisg];
}
if (FC_flash_attn_ext_bc_mask) {
sm2[j*SH + tiisg] = (iq1 + j) < args.ne31 ? pm2[jj][tiisg] : half2(-MAXHALF, -MAXHALF);
} else {
sm2[j*SH + tiisg] = pm2[jj][tiisg];
}

pm2[jj] += NW;
pm2[jj] += NW;
}
} else if (blk_cur == 2) {
FOR_UNROLL (short jj = 0; jj < NQ; ++jj) {
pm2[jj] += NW;
}
}

#if 0
Expand Down Expand Up @@ -5752,10 +5765,12 @@ void kernel_flash_attn_ext_impl(
}

// mqk = mqk + slope*mask
if (FC_flash_attn_ext_has_bias) {
s2 += s2_t(sm2[j*SH + tiisg])*slope;
} else {
s2 += s2_t(sm2[j*SH + tiisg]);
if (blk_cur != 2) {
if (FC_flash_attn_ext_has_bias) {
s2 += s2_t(sm2[j*SH + tiisg])*slope;
} else {
s2 += s2_t(sm2[j*SH + tiisg]);
}
}

M[jj] = simd_max(max(M[jj], max(s2[0], s2[1])));
Expand Down
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