Re: [Intel-gfx] [PATCH i-g-t 05/17] lib: Spin fast, retire early

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 02/07/2018 10:07, 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.
> 
> v2: Don't change perf_pmu as that is sensitive to the extra CPU latency
> from a tight GPU spinner.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Reviewed-by: Antonio Argenziano <antonio.argenziano@intel.com> #v1
> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> #v1
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   lib/igt_dummyload.c       | 3 ++-
>   lib/igt_dummyload.h       | 1 +
>   tests/gem_ctx_isolation.c | 1 +
>   tests/gem_eio.c           | 1 +
>   tests/gem_exec_latency.c  | 4 ++--
>   5 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/igt_dummyload.c b/lib/igt_dummyload.c
> index 94efdf745..7beb66244 100644
> --- a/lib/igt_dummyload.c
> +++ b/lib/igt_dummyload.c
> @@ -199,7 +199,8 @@ emit_recursive_batch(igt_spin_t *spin,
>   	 * 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 (!(opts->flags & IGT_SPIN_FAST))
> +		batch += 1000;

igt_require(!snb) or something, given the comment whose last two lines 
can be seen in the diff above?

Regards,

Tvrtko

>   
>   	/* recurse */
>   	r = &relocs[obj[BATCH].relocation_count++];
> diff --git a/lib/igt_dummyload.h b/lib/igt_dummyload.h
> index c794f2544..e80a12451 100644
> --- a/lib/igt_dummyload.h
> +++ b/lib/igt_dummyload.h
> @@ -52,6 +52,7 @@ struct igt_spin_factory {
>   
>   #define IGT_SPIN_FENCE_OUT (1 << 0)
>   #define IGT_SPIN_POLL_RUN  (1 << 1)
> +#define IGT_SPIN_FAST      (1 << 2)
>   
>   igt_spin_t *
>   __igt_spin_batch_factory(int fd, const struct igt_spin_factory *opts);
> diff --git a/tests/gem_ctx_isolation.c b/tests/gem_ctx_isolation.c
> index 2e19e8c03..4325e1c28 100644
> --- a/tests/gem_ctx_isolation.c
> +++ b/tests/gem_ctx_isolation.c
> @@ -560,6 +560,7 @@ static void inject_reset_context(int fd, unsigned int engine)
>   	struct igt_spin_factory opts = {
>   		.ctx = gem_context_create(fd),
>   		.engine = engine,
> +		.flags = IGT_SPIN_FAST,
>   	};
>   	igt_spin_t *spin;
>   
> diff --git a/tests/gem_eio.c b/tests/gem_eio.c
> index 0ec1aaec9..3162a3170 100644
> --- a/tests/gem_eio.c
> +++ b/tests/gem_eio.c
> @@ -160,6 +160,7 @@ static igt_spin_t * __spin_poll(int fd, uint32_t ctx, unsigned long flags)
>   	struct igt_spin_factory opts = {
>   		.ctx = ctx,
>   		.engine = flags,
> +		.flags = IGT_SPIN_FAST,
>   	};
>   
>   	if (gem_can_store_dword(fd, opts.engine))
> diff --git a/tests/gem_exec_latency.c b/tests/gem_exec_latency.c
> index 75811f325..de16322a6 100644
> --- a/tests/gem_exec_latency.c
> +++ b/tests/gem_exec_latency.c
> @@ -65,7 +65,7 @@ poll_ring(int fd, unsigned ring, const char *name)
>   {
>   	const struct igt_spin_factory opts = {
>   		.engine = ring,
> -		.flags = IGT_SPIN_POLL_RUN,
> +		.flags = IGT_SPIN_POLL_RUN | IGT_SPIN_FAST,
>   	};
>   	struct timespec tv = {};
>   	unsigned long cycles;
> @@ -464,7 +464,7 @@ rthog_latency_on_ring(int fd, unsigned int engine, const char *name, unsigned in
>   #define MMAP_SZ (64 << 10)
>   	const struct igt_spin_factory opts = {
>   		.engine = engine,
> -		.flags = IGT_SPIN_POLL_RUN,
> +		.flags = IGT_SPIN_POLL_RUN | IGT_SPIN_FAST,
>   	};
>   	struct rt_pkt *results;
>   	unsigned int engines[16];
> 
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