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Date:   Sun, 17 Oct 2021 20:36:46 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     German Gomez <german.gomez@....com>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Mike Leach <mike.leach@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org
Subject: Re: [PATCH 4/5] perf arm-spe: Implement find_snapshot callback

On Sun, Oct 17, 2021 at 08:05:46PM +0800, Leo Yan wrote:

[...]


> To allow arm_spe_buffer_has_wrapped() to work properly, I think we
> need to clean up the top 8 bytes of the AUX buffer in Arm SPE driver
> when start the PMU event (please note, this change has an assumption
> that is meantioned in another email that suggests to remove redundant
> PERF_RECORD_AUX events so the function arm_spe_perf_aux_output_begin()
> is invoked only once when start PMU event, so we can use the top 8
> bytes in AUX buffer to indicate trace is wrap around or not).
> 
> 
> diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
> index d44bcc29d99c..eb35f85d0efb 100644
> --- a/drivers/perf/arm_spe_pmu.c
> +++ b/drivers/perf/arm_spe_pmu.c
> @@ -493,6 +493,16 @@ static void arm_spe_perf_aux_output_begin(struct perf_output_handle *handle,
>         if (limit)
>                 limit |= BIT(SYS_PMBLIMITR_EL1_E_SHIFT);
> 
> +       /*
> +        * Cleanup the top 8 bytes for snapshot mode; these 8 bytes are
> +        * used to indicate if trace data is wrap around if they are not
> +        * zero.
> +        */
> +       if (buf->snapshot) {
> +               void *tail = buf->base + (buf->nr_pages << PAGE_SHIFT) - 8;
> +               memset(tail, 0x0, 8);

Here need to add below code for flushing data cache:

                 flush_dcache_range((unsigned long)tail, (unsigned long)tail+8);

Sorry for spamming.

Leo

> +       }
> +
>         limit += (u64)buf->base;
>         base = (u64)buf->base + PERF_IDX2OFF(handle->head, buf);
>         write_sysreg_s(base, SYS_PMBPTR_EL1);

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