[host] dxgi: sleep until it's close to time to map

This change adds an average function to time how long it takes the GPU
to copy and map the texture, and then uses this average to sleep for 80%
of this average lowering CPU usage and potentially decreasing lock
contention.

host/platform/Windows/capture/DXGI/src/dxgi.c

@@ -26,6 +26,7 @@
 #include "common/locking.h"
 #include "common/event.h"
 #include "common/dpi.h"
+#include "common/runningavg.h"
 
 #include <assert.h>
 #include <stdatomic.h>
@@ -63,6 +64,7 @@ typedef struct Texture
   volatile enum TextureState state;
   ID3D11Texture2D          * tex;
   D3D11_MAPPED_SUBRESOURCE   map;
+  uint64_t                   copyTime;
 }
 Texture;
 
@@ -90,6 +92,9 @@ struct iface
   atomic_int                 texReady;
   bool                       needsRelease;
 
+  RunningAvg                 avgMapTime;
+  uint64_t                   usleepMapTime;
+
   CaptureGetPointerBuffer    getPointerBufferFn;
   CapturePostPointerBuffer   postPointerBufferFn;
   LGEvent                  * frameEvent;
@@ -185,6 +190,7 @@ static bool dxgi_create(CaptureGetPointerBuffer getPointerBufferFn, CapturePostP
   this->texture             = calloc(sizeof(struct Texture), this->maxTextures);
   this->getPointerBufferFn  = getPointerBufferFn;
   this->postPointerBufferFn = postPointerBufferFn;
+  this->avgMapTime          = runningavg_new(10);
   return true;
 }
 
@@ -221,6 +227,9 @@ static bool dxgi_init(void)
   this->texWIndex = 0;
   atomic_store(&this->texReady, 0);
 
+  runningavg_reset(this->avgMapTime);
+  this->usleepMapTime = 0;
+
   lgResetEvent(this->frameEvent);
 
   status = CreateDXGIFactory1(&IID_IDXGIFactory1, (void **)&this->factory);
@@ -700,6 +709,7 @@ static void dxgi_free(void)
 
   free(this->texture);
 
+  runningavg_free(&this->avgMapTime);
   free(this);
   this = NULL;
 }
@@ -821,6 +831,7 @@ static CaptureResult dxgi_capture(void)
       if (copyFrame)
       {
         // issue the copy from GPU to CPU RAM
+        tex->copyTime = microtime();
         ID3D11DeviceContext_CopyResource(this->deviceContext,
           (ID3D11Resource *)tex->tex, (ID3D11Resource *)src);
       }
@@ -935,6 +946,11 @@ static CaptureResult dxgi_waitFrame(CaptureFrame * frame)
 
   Texture * tex = &this->texture[this->texRIndex];
 
+  // sleep until it's close to time to map
+  const uint64_t delta = microtime() - tex->copyTime;
+  if (delta < this->usleepMapTime)
+    usleep(this->usleepMapTime - delta);
+
   // try to map the resource, but don't wait for it
   for (int i = 0; ; ++i)
   {
@@ -958,6 +974,10 @@ static CaptureResult dxgi_waitFrame(CaptureFrame * frame)
     break;
   }
 
+  // update the sleep average and sleep for 80% of the average on the next call
+  runningavg_push(this->avgMapTime, microtime() - tex->copyTime);
+  this->usleepMapTime = (uint64_t)(runningavg_calc(this->avgMapTime) * 0.8);
+
   tex->state = TEXTURE_STATE_MAPPED;
 
   frame->formatVer = tex->formatVer;