Re: [PATCH] perf test: Increase buffer size for Coresight basic tests

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

On 3/26/24 17:07, James Clark wrote:
> These tests record in a mode that includes kernel trace but look for
> samples of a userspace process. This makes them sensitive to any kernel
> compilation options that increase the amount of time spent in the
> kernel. If the trace buffer is completely filled before userspace is
> reached then the test will fail. Double the buffer size to fix this.

This is a valid concern to address, but just wondering how did we arrive
at the conclusion that doubling the buffer size i.e making that 8M will
solve the problem positively for vast number of kerne build scenarios ?

> 
> The other tests in the same file aren't sensitive to this for various
> reasons, for example the iterate devices test filters by userspace
> trace only. But in order to keep coverage of all the modes, increase the
> buffer size rather than filtering by userspace for the basic tests.
> 
> Fixes: d1efa4a0a696 ("perf cs-etm: Add separate decode paths for timeless and per-thread modes")
> Signed-off-by: James Clark <james.clark@arm.com>
> ---
>  tools/perf/tests/shell/test_arm_coresight.sh | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/tests/shell/test_arm_coresight.sh b/tools/perf/tests/shell/test_arm_coresight.sh
> index 65dd85207125..3302ea0b9672 100755
> --- a/tools/perf/tests/shell/test_arm_coresight.sh
> +++ b/tools/perf/tests/shell/test_arm_coresight.sh
> @@ -188,7 +188,7 @@ arm_cs_etm_snapshot_test() {
>  
>  arm_cs_etm_basic_test() {
>  	echo "Recording trace with '$*'"
> -	perf record -o ${perfdata} "$@" -- ls > /dev/null 2>&1
> +	perf record -o ${perfdata} "$@" -m,8M -- ls > /dev/null 2>&1
>  
>  	perf_script_branch_samples ls &&
>  	perf_report_branch_samples ls &&