Quoting Lionel Landwerlin (2020-03-30 10:14:11)
> Reading or writing those fields should only happen under
> stream->oa_buffer.ptr_lock.
Writing, yes. Reading as a pair, sure. There are other ways you can
ensure that the tail/head are read as one, but fair enough.
> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
> Fixes: d1df41eb72ef ("drm/i915/perf: rework aging tail workaround")
> ---
> drivers/gpu/drm/i915/i915_perf.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
> index c74ebac50015..ec9421f02ebd 100644
> --- a/drivers/gpu/drm/i915/i915_perf.c
> +++ b/drivers/gpu/drm/i915/i915_perf.c
> @@ -463,6 +463,7 @@ static bool oa_buffer_check_unlocked(struct i915_perf_stream *stream)
> u32 gtt_offset = i915_ggtt_offset(stream->oa_buffer.vma);
> int report_size = stream->oa_buffer.format_size;
> unsigned long flags;
> + bool pollin;
> u32 hw_tail;
> u64 now;
>
> @@ -532,10 +533,13 @@ static bool oa_buffer_check_unlocked(struct i915_perf_stream *stream)
> stream->oa_buffer.aging_timestamp = now;
> }
>
> + pollin = OA_TAKEN(stream->oa_buffer.tail - gtt_offset,
> + stream->oa_buffer.head - gtt_offset) >= report_size;
> +
> +
Bonus \n
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> spin_unlock_irqrestore(&stream->oa_buffer.ptr_lock, flags);
>
> - return OA_TAKEN(stream->oa_buffer.tail - gtt_offset,
> - stream->oa_buffer.head - gtt_offset) >= report_size;
> + return pollin;
You could always leave the calculation here, and just have the read
inside.
-Chris
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