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metal : add env var to trigger graph capture #20398

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Merged
ggerganov merged 1 commit into from
Mar 11, 2026
Merged

metal : add env var to trigger graph capture #20398

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29 changes: 22 additions & 7 deletions ggml/src/ggml-metal/ggml-metal-context.m
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Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,7 @@
uint64_t fuse_cnt[GGML_OP_COUNT];

// capture state
bool capture_next_compute;
int capture_compute;
bool capture_started;

id<MTLCaptureScope> capture_scope;
Expand Down Expand Up @@ -158,10 +158,17 @@ ggml_metal_t ggml_metal_init(ggml_metal_device_t dev) {
GGML_LOG_INFO("%s: use concurrency = %s\n", __func__, res->use_concurrency ? "true" : "false");
GGML_LOG_INFO("%s: use graph optimize = %s\n", __func__, res->use_graph_optimize ? "true" : "false");

res->capture_next_compute = false;
res->capture_compute = 0;
res->capture_started = false;
res->capture_scope = nil;

{
const char * val = getenv("GGML_METAL_CAPTURE_COMPUTE");
if (val) {
res->capture_compute = atoi(val);
}
}

res->has_error = false;

res->gf = nil;
Expand Down Expand Up @@ -458,9 +465,13 @@ enum ggml_status ggml_metal_graph_compute(ggml_metal_t ctx, struct ggml_cgraph *

ctx->n_nodes_per_cb = (ctx->n_nodes_1 + ctx->n_cb - 1) / ctx->n_cb;

const bool use_capture = ctx->capture_next_compute;
if (ctx->capture_compute > 0) {
ctx->capture_compute--;
}

const bool use_capture = ctx->capture_compute == 0;
if (use_capture) {
ctx->capture_next_compute = false;
ctx->capture_compute = -1;

// make sure all previous computations have finished before starting the capture
if (ctx->cmd_buf_last) {
Expand All @@ -469,14 +480,18 @@ enum ggml_status ggml_metal_graph_compute(ggml_metal_t ctx, struct ggml_cgraph *
}

if (!ctx->capture_started) {
NSString * path = [NSString stringWithFormat:@"/tmp/perf-metal-%d.gputrace", getpid()];

GGML_LOG_WARN("%s: capturing graph in %s\n", __func__, [path UTF8String]);

// create capture scope
id<MTLDevice> device = ggml_metal_device_get_obj(ctx->dev);
ctx->capture_scope = [[MTLCaptureManager sharedCaptureManager] newCaptureScopeWithDevice:device];

MTLCaptureDescriptor * descriptor = [MTLCaptureDescriptor new];
descriptor.captureObject = ctx->capture_scope;
descriptor.destination = MTLCaptureDestinationGPUTraceDocument;
descriptor.outputURL = [NSURL fileURLWithPath:[NSString stringWithFormat:@"/tmp/perf-metal.gputrace"]];
descriptor.outputURL = [NSURL fileURLWithPath:path];

NSError * error = nil;
if (![[MTLCaptureManager sharedCaptureManager] startCaptureWithDescriptor:descriptor error:&error]) {
Expand Down Expand Up @@ -683,7 +698,7 @@ void ggml_metal_set_n_cb(ggml_metal_t ctx, int n_cb) {
idx_end,
ctx->use_fusion,
ctx->use_concurrency,
ctx->capture_next_compute,
ctx->capture_compute,
ctx->debug_graph,
ctx->debug_fusion);

Expand Down Expand Up @@ -718,5 +733,5 @@ bool ggml_metal_supports_family(ggml_metal_t ctx, int family) {
}

void ggml_metal_capture_next_compute(ggml_metal_t ctx) {
ctx->capture_next_compute = true;
ctx->capture_compute = 1;
}
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