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

[James Clark <james.clark@arm.com>]

On 12/04/2024 08:04, Anshuman Khandual wrote:
> 
> 
> 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 ?
> 

Nobody else has reported anything yet, if it happens again we can always
increase it again if that is what the issue is. I had most of the kernel
debugging stuff turned on like memory debugging etc, which is probably
why I ran into it and 8MB fixed it for me. So I'm not sure if there is
much more that could be added.

>>
>> 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 &&