Re: [PATCH 19/19] perf: cs-etm: Set watermark for AUX trace

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 01/12/25 4:52 PM, Leo Yan wrote:
> The default watermark is half of the total buffer size. In many cases,
> the tool can not be notified with sufficient free space, especially when
> profiling with small AUX buffer (e.g., 64KiB).

Could not smaller AUX buffer be prevented for TRBE instead ?

> > Setting watermark to quarter of the buffer to notifies the tool to read
> data earlier and prevents the data loss.
> 
> Signed-off-by: Leo Yan <leo.yan@arm.com>
> ---
>  tools/perf/arch/arm/util/cs-etm.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
> index ea891d12f8f40beebf8dee1d3db71cad701f5666..649b8b0d0f92b4af45fb97db9da3c5ccf24a978b 100644
> --- a/tools/perf/arch/arm/util/cs-etm.c
> +++ b/tools/perf/arch/arm/util/cs-etm.c
> @@ -424,6 +424,13 @@ static int cs_etm_recording_options(struct auxtrace_record *itr,
>  		pr_debug2("%s snapshot size: %zu\n", CORESIGHT_ETM_PMU_NAME,
>  			  opts->auxtrace_snapshot_size);
>  
> +	if (!opts->auxtrace_snapshot_mode && !opts->auxtrace_sample_mode) {
> +		size_t aw = opts->auxtrace_mmap_pages * (size_t)page_size / 4;
> +		u32 aux_watermark = aw > UINT_MAX ? UINT_MAX : aw;
> +
> +		cs_etm_evsel->core.attr.aux_watermark = aux_watermark;
> +	}
> +
>  	/*
>  	 * To obtain the auxtrace buffer file descriptor, the auxtrace
>  	 * event must come first.
>