On Fri, Dec 12, 2014 at 04:13:03PM +0000, Dave Gordon wrote:
> static inline void intel_ring_advance(struct intel_engine_cs *ring)
> {
> struct intel_ringbuffer *ringbuf = ring->buffer;
> - ringbuf->tail &= ringbuf->size - 1;
> +
> + __intel_ringbuffer_check(ringbuf);
> +
> + /*
> + * Tail == effecive_size is legitimate (buffer exactly full).
> + * Tail > effective_size is not, and should give a warning,
> + * but we'll reset tail in both cases to prevent further chaos
> + */
> + if (ringbuf->tail >= ringbuf->effective_size)
> + ringbuf->tail -= ringbuf->effective_size;
Urm. No. If you never write into the reserved pair of cachelines at the
end of the ringbuffer but the hw reads garbage from it, you lose.
tail &= size - 1; is a nice description of how the hw works that is
suitable for inlining, with all the magic in begin().
The goal is to remove the duplicated logic from intel_lrc.c, use
requests completely, and remove the dri1 hangover. To repeat what I said
last time:
http://cgit.freedesktop.org/~ickle/linux-2.6/tree/drivers/gpu/drm/i915/intel_ringbuffer.c?h=requests#n2447
is where I want us to go, a single piece of logic for ring management.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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