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metal: update rms_norm kernel

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This commit double the speed of rms_norm operations by using 512 threads
per threadgroup, combining with SIMD primitives to minimize the need for
thread group barriers.
This commit is contained in:
lshzh-ww 2023-07-16 22:28:59 -04:00
parent bbce392890
commit 4088df14ca
2 changed files with 27 additions and 16 deletions
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4
ggml-metal.m
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@ -792,7 +792,7 @@ void ggml_metal_graph_compute(
const float eps = 1e-6f;
const int nth = 256;
const int nth = 512;
[encoder setComputePipelineState:ctx->pipeline_rms_norm];
[encoder setBuffer:id_src0 offset:offs_src0 atIndex:0];
@ -800,7 +800,7 @@ void ggml_metal_graph_compute(
[encoder setBytes:&ne00 length:sizeof( int64_t) atIndex:2];
[encoder setBytes:&nb01 length:sizeof(uint64_t) atIndex:3];
[encoder setBytes:&eps length:sizeof( float) atIndex:4];
[encoder setThreadgroupMemoryLength:nth*sizeof(float) atIndex:0];
[encoder setThreadgroupMemoryLength:nth/32*sizeof(float) atIndex:0];
const int64_t nrows = ggml_nrows(src0);

33
ggml-metal.metal
View file

@ -339,26 +339,33 @@ kernel void kernel_rms_norm(
threadgroup float * sum [[threadgroup(0)]],
uint tgpig[[threadgroup_position_in_grid]],
uint tpitg[[thread_position_in_threadgroup]],
uint sgitg[[simdgroup_index_in_threadgroup]],
uint tiisg[[thread_index_in_simdgroup]],
uint ntg[[threads_per_threadgroup]]) {
device const float * x = (device const float *) ((device const char *) src0 + tgpig*nb01);
device const float4 * x = (device const float4 *) ((device const char *) src0 + tgpig*nb01);
device const float * x_scalar = (device const float *) x;
float4 sumf=0;
float all_sum=0;
// parallel sum
sum[tpitg] = 0.0f;
for (int i00 = tpitg; i00 < ne00; i00 += ntg) {
sum[tpitg] += x[i00] * x[i00];
for (int i00 = tpitg; i00 < ne00/4; i00 += ntg) {
sumf += x[i00] * x[i00];
}
all_sum = sumf[0] + sumf[1] + sumf[2] + sumf[3];
all_sum = simd_sum(all_sum);
if (tiisg == 0) {
sum[sgitg] = all_sum;
}
// reduce
threadgroup_barrier(mem_flags::mem_threadgroup);
for (uint i = ntg/2; i > 0; i /= 2) {
// broadcast, simd group number is ntg / 32
for (int i = ntg / 32 / 2; i > 0; i /= 2) {
if (tpitg < i) {
sum[tpitg] += sum[tpitg + i];
}
threadgroup_barrier(mem_flags::mem_threadgroup);
}
// broadcast
if (tpitg == 0) {
for (int i = 4 * (ne00 / 4); i < ne00; i++) {sum[0] += x_scalar[i];}
sum[0] /= ne00;
}
@ -367,10 +374,14 @@ kernel void kernel_rms_norm(
const float mean = sum[0];
const float scale = 1.0f/sqrt(mean + eps);
device float * y = dst + tgpig*ne00;
for (int i00 = tpitg; i00 < ne00; i00 += ntg) {
device float4 * y = (device float4 *) (dst + tgpig*ne00);
device float * y_scalar = (device float *) y;
for (int i00 = tpitg; i00 < ne00/4; i00 += ntg) {
y[i00] = x[i00] * scale;
}
if (tpitg == 0) {
for (int i00 = 4 * (ne00 / 4); i00 < ne00; i00++) {y_scalar[i00] = x_scalar[i00] * scale;}
}
}
// putting them in the kernel cause a significant performance penalty