On to, 2016-04-28 at 17:24 +0100, Chris Wilson wrote: > With 5 rings and a flush, we need 192 bytes of space to emit the > breadcrumb and semaphores. However, we need some spare room the size of > the single largest packet (36 dwords, 144 bytes) to accommodate > wraparound giving a grand total of 336 bytes > > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Based on the IRC discussion, seems reasonable. Reviewed-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_ringbuffer.h | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h > index 2651fd5263eb..dbf64f8a2356 100644 > --- a/drivers/gpu/drm/i915/intel_ringbuffer.h > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h > @@ -484,10 +484,10 @@ static inline u32 intel_ring_get_tail(struct intel_ringbuffer *ringbuf) > /* > * Arbitrary size for largest possible 'add request' sequence. The code paths > * are complex and variable. Empirical measurement shows that the worst case > - * is ILK at 136 words. Reserving too much is better than reserving too little > - * as that allows for corner cases that might have been missed. So the figure > - * has been rounded up to 160 words. > + * is BDW at 192 bytes (6 + 6 + 36 dwords), then ILK at 136 bytes. However, > + * we need to allocate double the largest single packet within that emission > + * to account for tail wraparound (so 6 + 6 + 72 dwords for BDW). > */ > -#define MIN_SPACE_FOR_ADD_REQUEST 160 > +#define MIN_SPACE_FOR_ADD_REQUEST 336 > > #endif /* _INTEL_RINGBUFFER_H_ */ -- Joonas Lahtinen Open Source Technology Center Intel Corporation _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
