drm/i915: Skip the execlists CSB scan and rewrite if the ring is untouched
If the CSB head/tail pointers are unchanged, we can skip the update of
the CSB register afterwards.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170124110009.28947-5-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index f729568..99ab2d7 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -574,9 +574,12 @@
csb = readl(csb_mmio);
head = GEN8_CSB_READ_PTR(csb);
tail = GEN8_CSB_WRITE_PTR(csb);
+ if (head == tail)
+ break;
+
if (tail < head)
tail += GEN8_CSB_ENTRIES;
- while (head < tail) {
+ do {
unsigned int idx = ++head % GEN8_CSB_ENTRIES;
unsigned int status = readl(buf + 2 * idx);
@@ -601,7 +604,7 @@
GEM_BUG_ON(port[0].count == 0 &&
!(status & GEN8_CTX_STATUS_ACTIVE_IDLE));
- }
+ } while (head < tail);
writel(_MASKED_FIELD(GEN8_CSB_READ_PTR_MASK,
GEN8_CSB_WRITE_PTR(csb) << 8),