[igt-dev] [PATCH i-g-t 07/24] i915/gem_sync: Make switch-default asymmetric

[Tvrtko Ursulin]

On 22/03/2019 09:21, Chris Wilson wrote:
> To make the demonstration of the cheeky preemption more impactful, make
> the second context a nop to contrast the first being 1024
> MI_STORE_DWORD_IMM. Then if we execute and wait on the second context
> before executing the first, the client latency is even more drastically
> reduced.
> 
> To more clearly show any effect on wait reordering, measure the
> alternative path and present both.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>   tests/i915/gem_sync.c | 40 +++++++++++++++++++++++++++++-----------
>   1 file changed, 29 insertions(+), 11 deletions(-)
> 
> diff --git a/tests/i915/gem_sync.c b/tests/i915/gem_sync.c
> index fb209977d..3e4feff32 100644
> --- a/tests/i915/gem_sync.c
> +++ b/tests/i915/gem_sync.c
> @@ -651,7 +651,7 @@ switch_ring(int fd, unsigned ring, int num_children, int timeout)
>   			struct drm_i915_gem_relocation_entry reloc[1024];
>   			struct drm_i915_gem_execbuffer2 execbuf;
>   		} contexts[2];
> -		double start, elapsed;
> +		double elapsed, baseline;
>   		unsigned long cycles;
>   
>   		for (int i = 0; i < ARRAY_SIZE(contexts); i++) {
> @@ -679,7 +679,7 @@ switch_ring(int fd, unsigned ring, int num_children, int timeout)
>   			c->object[1].handle = gem_create(fd, sz);
>   
>   			c->object[1].relocs_ptr = to_user_pointer(c->reloc);
> -			c->object[1].relocation_count = 1024;
> +			c->object[1].relocation_count = 1024 * i;
>   
>   			batch = gem_mmap__cpu(fd, c->object[1].handle, 0, sz,
>   					PROT_WRITE | PROT_READ);
> @@ -688,7 +688,7 @@ switch_ring(int fd, unsigned ring, int num_children, int timeout)
>   
>   			memset(c->reloc, 0, sizeof(c->reloc));
>   			b = batch;
> -			for (int r = 0; r < 1024; r++) {
> +			for (int r = 0; r < c->object[1].relocation_count; r++) {
>   				uint64_t offset;
>   
>   				c->reloc[r].presumed_offset = c->object[0].offset;
> @@ -722,26 +722,44 @@ switch_ring(int fd, unsigned ring, int num_children, int timeout)
>   		}
>   
>   		cycles = 0;
> -		elapsed = 0;
> -		start = gettime();
> -		do {
> +		baseline = 0;
> +		igt_until_timeout(timeout) {
>   			do {
>   				double this;
>   
> -				gem_execbuf(fd, &contexts[0].execbuf);
>   				gem_execbuf(fd, &contexts[1].execbuf);
> +				gem_execbuf(fd, &contexts[0].execbuf);
>   
>   				this = gettime();
>   				gem_sync(fd, contexts[1].object[1].handle);
> -				elapsed += gettime() - this;
> +				gem_sync(fd, contexts[0].object[1].handle);
> +				baseline += gettime() - this;
> +			} while (++cycles & 1023);
> +		}
> +		baseline /= cycles;
> +
> +		cycles = 0;
> +		elapsed = 0;
> +		igt_until_timeout(timeout) {
> +			do {
> +				double this;
>   
> +				gem_execbuf(fd, &contexts[1].execbuf);
> +				gem_execbuf(fd, &contexts[0].execbuf);
> +
> +				this = gettime();
>   				gem_sync(fd, contexts[0].object[1].handle);
> +				elapsed += gettime() - this;
> +
> +				gem_sync(fd, contexts[1].object[1].handle);
>   			} while (++cycles & 1023);
> -		} while ((gettime() - start) < timeout);
> -		igt_info("%s%sompleted %ld cycles: %.3f us\n",
> +		}
> +		elapsed /= cycles;
> +
> +		igt_info("%s%sompleted %ld cycles: %.3f us, baseline %.3f us\n",
>   			 names[child % num_engines] ?: "",
>   			 names[child % num_engines] ? " c" : "C",
> -			 cycles, elapsed*1e6/cycles);
> +			 cycles, elapsed*1e6, baseline*1e6);
>   
>   		for (int i = 0; i < ARRAY_SIZE(contexts); i++) {
>   			gem_close(fd, contexts[i].object[1].handle);
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Regards,

Tvrtko