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

Tvrtko Ursulin
2019-03-26T09:57:26Z

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@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@intel.com>

Regards,

Tvrtko
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