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-rw-r--r--libdrm/intel/intel_bufmgr_fake.c115
1 files changed, 84 insertions, 31 deletions
diff --git a/libdrm/intel/intel_bufmgr_fake.c b/libdrm/intel/intel_bufmgr_fake.c
index 28c7f6b3..e26d46c1 100644
--- a/libdrm/intel/intel_bufmgr_fake.c
+++ b/libdrm/intel/intel_bufmgr_fake.c
@@ -166,7 +166,7 @@ typedef struct _bufmgr_fake {
/** Driver-supplied argument to driver callbacks */
void *driver_priv;
/* Pointer to kernel-updated sarea data for the last completed user irq */
- volatile unsigned int *last_dispatch;
+ volatile int *last_dispatch;
int fd;
@@ -264,61 +264,114 @@ _fence_emit_internal(dri_bufmgr_fake *bufmgr_fake)
abort();
}
- /* The kernel implementation of IRQ_WAIT is broken for wraparound, and has
- * been since it was first introduced. It only checks for
- * completed_seq >= seq, and thus returns success early for wrapped irq
- * values if the CPU wins a race.
- *
- * We have to do it up front at emit when we discover wrap, so that another
- * client can't race (after we drop the lock) to emit and wait and fail.
- */
- if (seq == 0 || seq == 1) {
- drmCommandWriteRead(bufmgr_fake->fd, DRM_I915_FLUSH, &ie, sizeof(ie));
- }
-
DBG("emit 0x%08x\n", seq);
bufmgr_fake->last_fence = seq;
return bufmgr_fake->last_fence;
}
static void
-_fence_wait_internal(dri_bufmgr_fake *bufmgr_fake, unsigned int cookie)
+_fence_wait_internal(dri_bufmgr_fake *bufmgr_fake, int seq)
{
struct drm_i915_irq_wait iw;
- unsigned int last_dispatch;
+ int hw_seq;
int ret;
+ int kernel_lied;
if (bufmgr_fake->fence_wait != NULL) {
- bufmgr_fake->fence_wait(cookie, bufmgr_fake->fence_priv);
+ bufmgr_fake->fence_wait(seq, bufmgr_fake->fence_priv);
return;
}
DBG("wait 0x%08x\n", iw.irq_seq);
- /* The kernel implementation of IRQ_WAIT is broken for wraparound, and has
- * been since it was first introduced. It only checks for
- * completed_seq >= seq, and thus never returns for pre-wrapped irq values
- * if the GPU wins the race.
+ iw.irq_seq = seq;
+
+ /* The kernel IRQ_WAIT implementation is all sorts of broken.
+ * 1) It returns 1 to 0x7fffffff instead of using the full 32-bit unsigned
+ * range.
+ * 2) It returns 0 if hw_seq >= seq, not seq - hw_seq < 0 on the 32-bit
+ * signed range.
+ * 3) It waits if seq < hw_seq, not seq - hw_seq > 0 on the 32-bit
+ * signed range.
+ * 4) It returns -EBUSY in 3 seconds even if the hardware is still
+ * successfully chewing through buffers.
+ *
+ * Assume that in userland we treat sequence numbers as ints, which makes
+ * some of the comparisons convenient, since the sequence numbers are
+ * all postive signed integers.
+ *
+ * From this we get several cases we need to handle. Here's a timeline.
+ * 0x2 0x7 0x7ffffff8 0x7ffffffd
+ * | | | |
+ * -------------------------------------------------------------------
+ *
+ * A) Normal wait for hw to catch up
+ * hw_seq seq
+ * | |
+ * -------------------------------------------------------------------
+ * seq - hw_seq = 5. If we call IRQ_WAIT, it will wait for hw to catch up.
+ *
+ * B) Normal wait for a sequence number that's already passed.
+ * seq hw_seq
+ * | |
+ * -------------------------------------------------------------------
+ * seq - hw_seq = -5. If we call IRQ_WAIT, it returns 0 quickly.
*
- * So, check if it looks like a pre-wrapped value and just return success.
+ * C) Hardware has already wrapped around ahead of us
+ * hw_seq seq
+ * | |
+ * -------------------------------------------------------------------
+ * seq - hw_seq = 0x80000000 - 5. If we called IRQ_WAIT, it would wait
+ * for hw_seq >= seq, which may never occur. Thus, we want to catch this
+ * in userland and return 0.
+ *
+ * D) We've wrapped around ahead of the hardware.
+ * seq hw_seq
+ * | |
+ * -------------------------------------------------------------------
+ * seq - hw_seq = -(0x80000000 - 5). If we called IRQ_WAIT, it would return
+ * 0 quickly because hw_seq >= seq, even though the hardware isn't caught up.
+ * Thus, we need to catch this early return in userland and bother the
+ * kernel until the hardware really does catch up.
+ *
+ * E) Hardware might wrap after we test in userland.
+ * hw_seq seq
+ * | |
+ * -------------------------------------------------------------------
+ * seq - hw_seq = 5. If we call IRQ_WAIT, it will likely see seq >= hw_seq
+ * and wait. However, suppose hw_seq wraps before we make it into the
+ * kernel. The kernel sees hw_seq >= seq and waits for 3 seconds then
+ * returns -EBUSY. This is case C). We should catch this and then return
+ * successfully.
*/
- if (*bufmgr_fake->last_dispatch - cookie > 0x4000000)
- return;
+ do {
+ /* Keep a copy of last_dispatch so that if the wait -EBUSYs because the
+ * hardware didn't catch up in 3 seconds, we can see if it at least made
+ * progress and retry.
+ */
+ hw_seq = *bufmgr_fake->last_dispatch;
- iw.irq_seq = cookie;
+ /* Catch case C */
+ if (seq - hw_seq > 0x40000000)
+ return;
- do {
- last_dispatch = *bufmgr_fake->last_dispatch;
ret = drmCommandWrite(bufmgr_fake->fd, DRM_I915_IRQ_WAIT,
&iw, sizeof(iw));
- } while (ret == -EAGAIN || ret == -EINTR ||
- (ret == -EBUSY && last_dispatch != *bufmgr_fake->last_dispatch));
+ /* Catch case D */
+ kernel_lied = (ret == 0) && (seq - *bufmgr_fake->last_dispatch <
+ -0x40000000);
+
+ /* Catch case E */
+ if (ret == -EBUSY && (seq - *bufmgr_fake->last_dispatch > 0x40000000))
+ ret = 0;
+ } while (kernel_lied || ret == -EAGAIN || ret == -EINTR ||
+ (ret == -EBUSY && hw_seq != *bufmgr_fake->last_dispatch));
if (ret != 0) {
drmMsg("%s:%d: Error %d waiting for fence.\n", __FILE__, __LINE__, ret);
abort();
}
- clear_fenced(bufmgr_fake, cookie);
+ clear_fenced(bufmgr_fake, seq);
}
static int
@@ -1312,7 +1365,7 @@ void intel_bufmgr_fake_set_last_dispatch(dri_bufmgr *bufmgr,
{
dri_bufmgr_fake *bufmgr_fake = (dri_bufmgr_fake *)bufmgr;
- bufmgr_fake->last_dispatch = last_dispatch;
+ bufmgr_fake->last_dispatch = (volatile int *)last_dispatch;
}
dri_bufmgr *
@@ -1349,7 +1402,7 @@ intel_bufmgr_fake_init(int fd,
bufmgr_fake->bufmgr.debug = 0;
bufmgr_fake->fd = fd;
- bufmgr_fake->last_dispatch = last_dispatch;
+ bufmgr_fake->last_dispatch = (volatile int *)last_dispatch;
return &bufmgr_fake->bufmgr;
}