On Wed, Apr 05, 2017 at 10:28:53AM -0700, Jason Ekstrand wrote:
> Before, we were just looking at whether or not the user wanted us to
> wait and waiting on the BO. Some clients, such as the Serious engine,
> use a single query pool for hundreds of individual query results where
> the writes for those queries may be split across several command
> buffers. In this scenario, the individual query we're looking for may
> become available long before the BO is idle so waiting on the query pool
> BO to be finished is wasteful. This commit makes us instead busy-loop on
> each query until it's available.
>
> This significantly reduces pipeline bubbles and improves performance of
> The Talos Principle on medium settings (where the GPU isn't overloaded
> with drawing) by around 20% on my SkyLake gt4.
> ---
> src/intel/vulkan/genX_query.c | 52
> ++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 46 insertions(+), 6 deletions(-)
>
> diff --git a/src/intel/vulkan/genX_query.c b/src/intel/vulkan/genX_query.c
> index 7ea9404..0d303a6 100644
> --- a/src/intel/vulkan/genX_query.c
> +++ b/src/intel/vulkan/genX_query.c
> @@ -131,6 +131,44 @@ cpu_write_query_result(void *dst_slot,
> VkQueryResultFlags flags,
> }
> }
>
> +static bool
> +query_is_available(struct anv_device *device, volatile uint64_t *slot)
> +{
> + if (!device->info.has_llc)
> + __builtin_ia32_clflush(slot);
> +
> + return slot[0];
> +}
> +
> +static VkResult
> +wait_for_available(struct anv_device *device,
> + struct anv_query_pool *pool, uint64_t *slot)
> +{
> + while (true) {
> + if (query_is_available(device, slot))
> + return VK_SUCCESS;
> +
> + VkResult result = anv_device_bo_busy(device, &pool->bo);
Ah, but you can use the simpler check here because you follow up with a
query_is_available() so you know whether or not the hang clobbered the
result.
If the query is not available but the bo is idle, you might then went to
check for a reset in case it was due to a lost device. GEM_BUSY is
lockless, but GEM_RESET_STATS currently takes the big struct_mutex and
so has non-deterministic and often quite large latencies.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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