From 092467327c45edbfce6c2bb71ee842bec16b9a60 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Sat, 10 Aug 2013 22:16:32 +0100 Subject: drm/i915: Write RING_TAIL once per-request Ignoring the legacy DRI1 code, and a couple of special cases (to be discussed later), all access to the ring is mediated through requests. The first write to a ring will grab a seqno and mark the ring as having an outstanding_lazy_request. Either through explicitly adding a request after an execbuffer or through an implicit wait (either by the CPU or by a semaphore), that sequence of writes will be terminated with a request. So we can ellide all the intervening writes to the tail register and send the entire command stream to the GPU at once. This will reduce the number of *serialising* writes to the tail register by a factor or 3-5 times (depending upon architecture and number of workarounds, context switches, etc involved). This becomes even more noticeable when the register write is overloaded with a number of debugging tools. The astute reader will wonder if it is then possible to overflow the ring with a single command. It is not. When we start a command sequence to the ring, we check for available space and issue a wait in case we have not. The ring wait will in this case be forced to flush the outstanding register write and then poll the ACTHD for sufficient space to continue. The exception to the rule where everything is inside a request are a few initialisation cases where we may want to write GPU commands via the CS before userspace wakes up and page flips. Signed-off-by: Chris Wilson Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/i915_dma.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/gpu/drm/i915/i915_dma.c') diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c index 3de60503378..f4f98957ce4 100644 --- a/drivers/gpu/drm/i915/i915_dma.c +++ b/drivers/gpu/drm/i915/i915_dma.c @@ -52,7 +52,7 @@ intel_ring_emit(LP_RING(dev_priv), x) #define ADVANCE_LP_RING() \ - intel_ring_advance(LP_RING(dev_priv)) + __intel_ring_advance(LP_RING(dev_priv)) /** * Lock test for when it's just for synchronization of ring access. -- cgit v1.2.3-18-g5258