[igt-dev] [PATCH i-g-t 1/2] lib: Spin fast, sweet chariot, coming to carry me home

[Antonio Argenziano]

On 19/06/18 06:55, Chris Wilson wrote:
> When using the pollable spinner, we often want to use it as a means of
> ensuring the task is running on the GPU before switching to something
> else. In which case we don't want to add extra delay inside the spinner,
> but the current 1000 NOPs add on order of 5us, which is often larger
> than the target latency.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

Reviewed-by: Antonio Argenziano <antonio.argenziano at intel.com>

> ---
>   lib/igt_dummyload.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/igt_dummyload.c b/lib/igt_dummyload.c
> index d32b421c6..b090b8004 100644
> --- a/lib/igt_dummyload.c
> +++ b/lib/igt_dummyload.c
> @@ -78,6 +78,7 @@ fill_reloc(struct drm_i915_gem_relocation_entry *reloc,
>   #define OUT_FENCE	(1 << 0)
>   #define POLL_RUN	(1 << 1)
>   #define NO_PREEMPTION   (1 << 2)
> +#define SPIN_FAST       (1 << 3)
>   
>   static int
>   emit_recursive_batch(igt_spin_t *spin, int fd, uint32_t ctx, unsigned engine,
> @@ -212,7 +213,8 @@ emit_recursive_batch(igt_spin_t *spin, int fd, uint32_t ctx, unsigned engine,
>   	 * between function calls, that appears enough to keep SNB out of
>   	 * trouble. See https://bugs.freedesktop.org/show_bug.cgi?id=102262
>   	 */
> -	batch += 1000;
> +	if (!(flags & SPIN_FAST))
> +		batch += 1000;
>   
>   	/* recurse */
>   	r = &relocs[obj[BATCH].relocation_count++];
> @@ -369,7 +371,7 @@ igt_spin_batch_new_fence(int fd, uint32_t ctx, unsigned engine)
>   igt_spin_t *
>   __igt_spin_batch_new_poll(int fd, uint32_t ctx, unsigned engine)
>   {
> -	return ___igt_spin_batch_new(fd, ctx, engine, 0, POLL_RUN);
> +	return ___igt_spin_batch_new(fd, ctx, engine, 0, POLL_RUN | SPIN_FAST);
>   }
>   
>   igt_spin_t *
>