[Mesa-dev] [PATCH] anv/query: Busy-wait for available query entries

[Jason Ekstrand]

Before, we were just looking at whether or not the user wanted us to
wait and waiting on the BO.  This instead makes us busy-loop on each
query until it's available.  This reduces some of the pipeline bubbles
we were getting and improves performance of The Talos Principle on
medium settings (where the GPU isn't overloaded) by around 20% on my
SkyLake gt4.
---
 src/intel/vulkan/genX_query.c | 72 +++++++++++++++++++++++++++++++++++++++----
 1 file changed, 66 insertions(+), 6 deletions(-)

diff --git a/src/intel/vulkan/genX_query.c b/src/intel/vulkan/genX_query.c
index 7ea9404..ebf99d2 100644
--- a/src/intel/vulkan/genX_query.c
+++ b/src/intel/vulkan/genX_query.c
@@ -131,6 +131,64 @@ cpu_write_query_result(void *dst_slot, VkQueryResultFlags flags,
    }
 }
 
+#define NSEC_PER_SEC 1000000000
+
+static bool
+query_is_available(struct anv_device *device, 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) {
+      struct timespec start;
+      clock_gettime(CLOCK_MONOTONIC, &start);
+
+      while (true) {
+         if (!device->info.has_llc)
+            __builtin_ia32_clflush(slot);
+
+         if (query_is_available(device, slot))
+            return VK_SUCCESS;
+
+         struct timespec current;
+         clock_gettime(CLOCK_MONOTONIC, &current);
+
+         if (current.tv_nsec < start.tv_nsec) {
+            current.tv_nsec += NSEC_PER_SEC;
+            current.tv_sec -= 1;
+         }
+
+         /* If we've been looping for more than 1 ms, break out of the busy
+          * loop and ask the kernel if the buffer is actually busy.
+          */
+         if (current.tv_sec > start.tv_sec ||
+             current.tv_nsec - start.tv_nsec > 1000000)
+            break;
+      }
+
+      VkResult result = anv_device_wait(device, &pool->bo, 0);
+      switch (result) {
+      case VK_SUCCESS:
+         /* The BO is no longer busy.  If we haven't seen availability yet,
+          * then we never will.
+          */
+         return query_is_available(device, slot) ? VK_SUCCESS : VK_NOT_READY;
+      case VK_TIMEOUT:
+         /* The BO is still busy, keep waiting. */
+         continue;
+      default:
+         return result;
+      }
+   }
+}
+
 VkResult genX(GetQueryPoolResults)(
     VkDevice                                    _device,
     VkQueryPool                                 queryPool,
@@ -154,12 +212,6 @@ VkResult genX(GetQueryPoolResults)(
    if (pData == NULL)
       return VK_SUCCESS;
 
-   if (flags & VK_QUERY_RESULT_WAIT_BIT) {
-      VkResult result = anv_device_wait(device, &pool->bo, INT64_MAX);
-      if (result != VK_SUCCESS)
-         return result;
-   }
-
    void *data_end = pData + dataSize;
 
    if (!device->info.has_llc) {
@@ -176,6 +228,14 @@ VkResult genX(GetQueryPoolResults)(
       /* Availability is always at the start of the slot */
       bool available = slot[0];
 
+      if (!available && (flags & VK_QUERY_RESULT_WAIT_BIT)) {
+         status = wait_for_available(device, pool, slot);
+         if (status != VK_SUCCESS)
+            return status;
+
+         available = true;
+      }
+
       /* From the Vulkan 1.0.42 spec:
        *
        *    "If VK_QUERY_RESULT_WAIT_BIT and VK_QUERY_RESULT_PARTIAL_BIT are
-- 
2.5.0.400.gff86faf