drm/nv50: Fix large 3D performance regression caused by the interchannel sync patches.

Reported-by: Christoph Bumiller <e0425955@student.tuwien.ac.at>
Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Tested-by: Maarten Maathuis <madman2003@gmail.com>
Tested-by: Xavier Chantry <chantry.xavier@gmail.com>
Tested-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

diff --git a/drivers/gpu/drm/nouveau/nouveau_drv.h b/drivers/gpu/drm/nouveau/nouveau_drv.h
index a308c132c19be9833d9158e4771aa0995df0d067..3a07e580d27af548fe2fd247b4e7df4c67994956 100644 (file)
--- a/drivers/gpu/drm/nouveau/nouveau_drv.h
+++ b/drivers/gpu/drm/nouveau/nouveau_drv.h
@@ -1473,6 +1473,7 @@ nv_match_device(struct drm_device *dev, unsigned device,
 #define NV_SW_SEMAPHORE_OFFSET                                       0x00000064
 #define NV_SW_SEMAPHORE_ACQUIRE                                      0x00000068
 #define NV_SW_SEMAPHORE_RELEASE                                      0x0000006c
+#define NV_SW_YIELD                                                  0x00000080
 #define NV_SW_DMA_VBLSEM                                             0x0000018c
 #define NV_SW_VBLSEM_OFFSET                                          0x00000400
 #define NV_SW_VBLSEM_RELEASE_VALUE                                   0x00000404

diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
index f42675cc9d143609c377cfede5e5d4ae4c15c814..441b12420bb1b713fb56b98edad389d31fe367ea 100644 (file)
--- a/drivers/gpu/drm/nouveau/nouveau_fence.c
+++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
@@ -308,21 +308,54 @@ emit_semaphore(struct nouveau_channel *chan, int method,
 {
        struct drm_nouveau_private *dev_priv = sema->dev->dev_private;
        struct nouveau_fence *fence;
+       bool smart = (dev_priv->card_type >= NV_50);
        int ret;
 
-       ret = RING_SPACE(chan, dev_priv->card_type >= NV_50 ? 6 : 4);
+       ret = RING_SPACE(chan, smart ? 8 : 4);
        if (ret)
                return ret;
 
-       if (dev_priv->card_type >= NV_50) {
+       if (smart) {
                BEGIN_RING(chan, NvSubSw, NV_SW_DMA_SEMAPHORE, 1);
                OUT_RING(chan, NvSema);
        }
        BEGIN_RING(chan, NvSubSw, NV_SW_SEMAPHORE_OFFSET, 1);
        OUT_RING(chan, sema->mem->start);
+
+       if (smart && method == NV_SW_SEMAPHORE_ACQUIRE) {
+               /*
+                * NV50 tries to be too smart and context-switch
+                * between semaphores instead of doing a "first come,
+                * first served" strategy like previous cards
+                * do.
+                *
+                * That's bad because the ACQUIRE latency can get as
+                * large as the PFIFO context time slice in the
+                * typical DRI2 case where you have several
+                * outstanding semaphores at the same moment.
+                *
+                * If we're going to ACQUIRE, force the card to
+                * context switch before, just in case the matching
+                * RELEASE is already scheduled to be executed in
+                * another channel.
+                */
+               BEGIN_RING(chan, NvSubSw, NV_SW_YIELD, 1);
+               OUT_RING(chan, 0);
+       }
+
        BEGIN_RING(chan, NvSubSw, method, 1);
        OUT_RING(chan, 1);
 
+       if (smart && method == NV_SW_SEMAPHORE_RELEASE) {
+               /*
+                * Force the card to context switch, there may be
+                * another channel waiting for the semaphore we just
+                * released.
+                */
+               BEGIN_RING(chan, NvSubSw, NV_SW_YIELD, 1);
+               OUT_RING(chan, 0);
+       }
+
        /* Delay semaphore destruction until its work is done */
        ret = nouveau_fence_new(chan, &fence, true);
        if (ret)
@@ -355,14 +388,13 @@ nouveau_fence_sync(struct nouveau_fence *fence,
                return nouveau_fence_wait(fence, NULL, false, false);
        }
 
-       /* Signal the semaphore from chan */
-       ret = emit_semaphore(chan, NV_SW_SEMAPHORE_RELEASE, sema);
-       if (ret)
-               goto out;
-
        /* Make wchan wait until it gets signalled */
        ret = emit_semaphore(wchan, NV_SW_SEMAPHORE_ACQUIRE, sema);
+       if (ret)
+               goto out;
 
+       /* Signal the semaphore from chan */
+       ret = emit_semaphore(chan, NV_SW_SEMAPHORE_RELEASE, sema);
 out:
        kref_put(&sema->ref, free_semaphore);
        return ret;