Re: [PATCH] drm/i915/perf: Clear out entire reports after reading if not power of 2 size

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On Mon, May 22, 2023 at 02:50:51PM -0700, Dixit, Ashutosh wrote:
On Mon, 22 May 2023 14:34:18 -0700, Umesh Nerlige Ramappa wrote:

On Mon, May 22, 2023 at 01:17:49PM -0700, Ashutosh Dixit wrote:
> Clearing out report id and timestamp as means to detect unlanded reports
> only works if report size is power of 2. That is, only when report size is
> a sub-multiple of the OA buffer size can we be certain that reports will
> land at the same place each time in the OA buffer (after rewind). If report
> size is not a power of 2, we need to zero out the entire report to be able
> to detect unlanded reports reliably.
>
> Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx>
> Signed-off-by: Ashutosh Dixit <ashutosh.dixit@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_perf.c | 17 +++++++++++------
> 1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
> index 19d5652300eeb..58284156428dc 100644
> --- a/drivers/gpu/drm/i915/i915_perf.c
> +++ b/drivers/gpu/drm/i915/i915_perf.c
> @@ -877,12 +877,17 @@ static int gen8_append_oa_reports(struct i915_perf_stream *stream,
>			stream->oa_buffer.last_ctx_id = ctx_id;
>		}
>
> -		/*
> -		 * Clear out the report id and timestamp as a means to detect unlanded
> -		 * reports.
> -		 */
> -		oa_report_id_clear(stream, report32);
> -		oa_timestamp_clear(stream, report32);
> +		if (is_power_of_2(report_size)) {
> +			/*
> +			 * Clear out the report id and timestamp as a means
> +			 * to detect unlanded reports.
> +			 */
> +			oa_report_id_clear(stream, report32);
> +			oa_timestamp_clear(stream, report32);
> +		} else {
> +			/* Zero out the entire report */
> +			memset(report32, 0, report_size);

Indeed, this was a bug. For a minute, I started wondering if this is the
issue I am running into with the other patch posted for DG2, but then I see
the issue within the first fill of the OA buffer where chunks of the
reports are zeroed out, so this is a new issue.

Yes I saw this while reviewing your patch. And also I thought your issue
was happening on DG2 with power of 2 report size, only on MTL OAM we
introduce non power of 2 report size.

lgtm,

Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@xxxxxxxxx>

Maybe this should include Fixes: tag pointing to the patch that introduced the OAM non-power-of-2 format.

Umesh


Thanks.
--
Ashutosh


> +		}
>	}
>
>	if (start_offset != *offset) {
> --
> 2.38.0
>



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