On Thu, May 04, 2017 at 02:08:44PM +0100, Chris Wilson wrote: > Exploit the power-of-two ring size to compute the space across the > wraparound using a mask rather than a if. Convert to unsigned integers > so the operation is well defined. > > References: https://bugs.freedesktop.org/show_bug.cgi?id=99671 > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx> > Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_ringbuffer.c | 23 +++++++++++---------- > drivers/gpu/drm/i915/intel_ringbuffer.h | 36 ++++++++++++++++++++------------- > 2 files changed, 34 insertions(+), 25 deletions(-) > > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c > index 3ce1c87dec46..e7ef04cc071b 100644 > --- a/drivers/gpu/drm/i915/intel_ringbuffer.c > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c > @@ -39,12 +39,16 @@ > */ > #define LEGACY_REQUEST_SIZE 200 > > -static int __intel_ring_space(int head, int tail, int size) > +static unsigned int __intel_ring_space(unsigned int head, > + unsigned int tail, > + unsigned int size) > { > - int space = head - tail; > - if (space <= 0) > - space += size; > - return space - I915_RING_FREE_SPACE; > + /* > + * "If the Ring Buffer Head Pointer and the Tail Pointer are on the > + * same cacheline, the Head Pointer must not be greater than the Tail > + * Pointer." > + */ > + return (head - tail - CACHELINE_BYTES) & (size - 1); Btw, as you exploit power-of-two ring size here, maybe it is worth to repeat GEM_BUG_ON(!is_power_of_2(size)); to emphase this assumption in the code (not only in the commit message)? -Michal _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
