Re: [PATCH 4/5] perf arm-spe: Implement find_snapshot callback

Leo Yan
2021-10-17T12:36:55Z

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);