[Mesa-dev] [PATCH 4/4] i965: Fix remaining flush vs invalidate race conditions in brw_emit_pipe_control_flush.

[Jason Ekstrand]

3 and 4 are

Cc: "12.0 11.1 11.2" <mesa-stable at lists.freedesktop.org>
Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>

I did look over 3 fairly carefully.

It's worth noting that I think we have some double-pipe-controls that could
probably be put together now.  Not sure that we actually want to do that
though.
--Jason

On Thu, Jun 30, 2016 at 10:07 PM, Francisco Jerez <currojerez at riseup.net>
wrote:

> This hardware race condition has caused problems several times already
> (see "i965: Fix cache pollution race during L3 partitioning set-up.",
> "i965: Fix brw_render_cache_set_check_flush's PIPE_CONTROLs." and
> "i965: intel_texture_barrier reimplemented").  The problem is that
> whenever we attempt to both flush and invalidate multiple caches with
> a single pipe control command the flush and invalidation happen in
> reverse order, so the contents flushed from the R/W caches aren't
> guaranteed to become visible from the invalidated caches after the
> PIPE_CONTROL command completes execution if some concurrent rendering
> workload happened to pollute any of the invalidated R/O caches in the
> short window of time between the invalidation and flush.
>
> This makes sure that brw_emit_pipe_control_flush() has the effect
> expected by most callers of making the contents flushed from any R/W
> caches visible from the invalidated R/O caches.
> ---
>  src/mesa/drivers/dri/i965/brw_pipe_control.c | 18 ++++++++++++++++++
>  src/mesa/drivers/dri/i965/intel_reg.h        |  9 +++++++++
>  2 files changed, 27 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_pipe_control.c
> b/src/mesa/drivers/dri/i965/brw_pipe_control.c
> index 14a8f7c..05e8c05 100644
> --- a/src/mesa/drivers/dri/i965/brw_pipe_control.c
> +++ b/src/mesa/drivers/dri/i965/brw_pipe_control.c
> @@ -96,6 +96,24 @@ gen7_cs_stall_every_four_pipe_controls(struct
> brw_context *brw, uint32_t flags)
>  void
>  brw_emit_pipe_control_flush(struct brw_context *brw, uint32_t flags)
>  {
> +   if (brw->gen >= 6 &&
> +       (flags & PIPE_CONTROL_CACHE_FLUSH_BITS) &&
> +       (flags & PIPE_CONTROL_CACHE_INVALIDATE_BITS)) {
> +      /* A pipe control command with flush and invalidate bits set
> +       * simultaneously is an inherently racy operation on Gen6+ if the
> +       * contents of the flushed caches were intended to become visible
> from
> +       * any of the invalidated caches.  Split it in two PIPE_CONTROLs,
> the
> +       * first one should stall the pipeline to make sure that the
> flushed R/W
> +       * caches are coherent with memory once the specified R/O caches are
> +       * invalidated.  On pre-Gen6 hardware the (implicit) R/O cache
> +       * invalidation seems to happen at the bottom of the pipeline
> together
> +       * with any write cache flush, so this shouldn't be a concern.
> +       */
> +      brw_emit_pipe_control_flush(brw, (flags &
> PIPE_CONTROL_CACHE_FLUSH_BITS) |
> +                                       PIPE_CONTROL_CS_STALL);
> +      flags &= ~(PIPE_CONTROL_CACHE_FLUSH_BITS | PIPE_CONTROL_CS_STALL);
> +   }
> +
>     if (brw->gen >= 8) {
>        if (brw->gen == 8)
>           gen8_add_cs_stall_workaround_bits(&flags);
> diff --git a/src/mesa/drivers/dri/i965/intel_reg.h
> b/src/mesa/drivers/dri/i965/intel_reg.h
> index 95365fe..7a82be4 100644
> --- a/src/mesa/drivers/dri/i965/intel_reg.h
> +++ b/src/mesa/drivers/dri/i965/intel_reg.h
> @@ -134,6 +134,15 @@
>  #define PIPE_CONTROL_PPGTT_WRITE       (0 << 2)
>  #define PIPE_CONTROL_GLOBAL_GTT_WRITE  (1 << 2)
>
> +#define PIPE_CONTROL_CACHE_FLUSH_BITS \
> +   (PIPE_CONTROL_DEPTH_CACHE_FLUSH | PIPE_CONTROL_DATA_CACHE_FLUSH | \
> +    PIPE_CONTROL_RENDER_TARGET_FLUSH)
> +
> +#define PIPE_CONTROL_CACHE_INVALIDATE_BITS \
> +   (PIPE_CONTROL_STATE_CACHE_INVALIDATE |
> PIPE_CONTROL_CONST_CACHE_INVALIDATE | \
> +    PIPE_CONTROL_VF_CACHE_INVALIDATE |
> PIPE_CONTROL_TEXTURE_CACHE_INVALIDATE | \
> +    PIPE_CONTROL_INSTRUCTION_INVALIDATE)
> +
>  /** @} */
>
>  #define XY_SETUP_BLT_CMD               (CMD_2D | (0x01 << 22))
> --
> 2.9.0
>
>
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