Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> Part of the attraction of using a recursive batch is that it is
> hard on the system (executing the "function" call is apparently
> quite expensive). However, the GPU may hog the entire system for
> a few minutes, preventing even NMI. Quite why this is so is unclear,
> but presumably it relates to the PM_INTRMSK workaround on gen6/gen7.
> If we give the system a break by having the GPU execute a few nops
> between function calls, that appears enough to keep SNB out of
> trouble.
>
Can we trip into the same pit with igt_hang? It has tight
recurse. Adding few noops makes the hangcheck sampler
to hit more sparsely and slow the verdict of hang.
But we can then improve the heuristics ;)
-Mika
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Tomi Sarvela <tomi.p.sarvela@xxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> ---
> lib/igt_dummyload.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/lib/igt_dummyload.c b/lib/igt_dummyload.c
> index 00c6a030..c6e57cff 100644
> --- a/lib/igt_dummyload.c
> +++ b/lib/igt_dummyload.c
> @@ -103,7 +103,7 @@ static void emit_recursive_batch(igt_spin_t *spin,
> /* dummy write to dependency */
> obj[SCRATCH].handle = dep;
> fill_reloc(&relocs[obj[BATCH].relocation_count++],
> - dep, 256,
> + dep, 1020,
> I915_GEM_DOMAIN_RENDER,
> I915_GEM_DOMAIN_RENDER);
> execbuf.buffer_count++;
> @@ -112,9 +112,23 @@ static void emit_recursive_batch(igt_spin_t *spin,
> spin->batch = batch;
> spin->handle = obj[BATCH].handle;
>
> + /* Pad with a few nops so that we do not completely hog the system.
> + *
> + * Part of the attraction of using a recursive batch is that it is
> + * hard on the system (executing the "function" call is apparently
> + * quite expensive). However, the GPU may hog the entire system for
> + * a few minutes, preventing even NMI. Quite why this is so is unclear,
> + * but presumably it relates to the PM_INTRMSK workaround on gen6/gen7.
> + * If we give the system a break by having the GPU execute a few nops
> + * between function calls, that appears enough to keep SNB out of
> + * trouble. See https://
> + */
> + batch += 1000;
> +
> /* recurse */
> fill_reloc(&relocs[obj[BATCH].relocation_count],
> - obj[BATCH].handle, 1, I915_GEM_DOMAIN_COMMAND, 0);
> + obj[BATCH].handle, (batch - spin->batch) + 1,
> + I915_GEM_DOMAIN_COMMAND, 0);
> if (gen >= 8) {
> *batch++ = MI_BATCH_BUFFER_START | 1 << 8 | 1;
> *batch++ = 0;
> --
> 2.14.1
>
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