Re: [PATCH v4 18/19] perf test cs-etm: Speed up disassembly test

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Reducing `--stop-sample` to 2 causes the disassembly tests to spuriously fail on multi-core systems because the Python decoder limits the raw number of decoded events rather than objdump calls.
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commit 4c3c2bcace55cfb656bbb5453c90886308b6f40e
Author: James Clark <james.clark@linaro.org>

perf test cs-etm: Speed up disassembly test

This commit speeds up the coresight disassembly tests by using exit
snapshots to limit the amount of trace decoded, and by reducing the
stop-sample limit from 30 to 2 for both kernel and userspace testing.

> diff --git a/tools/perf/tests/shell/test_arm_coresight_disasm.sh b/tools/perf/tests/shell/test_arm_coresight_disasm.sh
> index f78dfb6bf73e3..f2fb1aa92252a 100755
> --- a/tools/perf/tests/shell/test_arm_coresight_disasm.sh
> +++ b/tools/perf/tests/shell/test_arm_coresight_disasm.sh
[ ... ]
> @@ -43,9 +43,9 @@ branch_search='[[:space:]](bl|b(\.(eq|ne|cs|cc|mi|pl|vs|vc|hi|ls|ge|lt|gt|le|al)
>  ## Test kernel ##
>  if [ "$(id -u)" == 0 ] && [ -e /proc/kcore ]; then
>  	echo "Testing kernel disassembly"
> -	perf record -o ${perfdata} -e cs_etm//k --kcore -- touch $file > /dev/null 2>&1
> +	perf record -o ${perfdata} -e cs_etm//k --kcore -Se -m,64K -- touch $file > /dev/null 2>&1
>  	perf script -i ${perfdata} -s python:${script_path} -- \
> -		-d --stop-sample=30 -k ${perfdata}/kcore_dir/kcore 2> /dev/null > ${file}
> +		-d --stop-sample=2 -k ${perfdata}/kcore_dir/kcore 2> /dev/null > ${file}

[Severity: Medium]
Will this reduced sample limit cause spurious test failures on multi-core
systems?

The Python decoder (arm-cs-trace-disasm.py) increments a global index for
every processed event, regardless of CPU. Printing disassembly for a single
basic block requires at least two events from the same CPU (one to
initialize the address cache, the next to construct the range and call
print_disam()).

With events interleaved across CPUs, and cs_etm synthesizing both
instructions and branches, could the 3-event limit (indexes 0, 1, 2) be
exhausted by cache initializations or non-branch events before a single
print_disam() call occurs? If the script exits before generating any
disassembly, the grep check below would fail.

>  	grep -q -E ${branch_search} ${file}
>  	echo "Found kernel branches"
>  else
[ ... ]
> @@ -55,9 +55,9 @@ fi
>  
>  ## Test user ##
>  echo "Testing userspace disassembly"
> -perf record -o ${perfdata} -e cs_etm//u -- touch $file > /dev/null 2>&1
> +perf record -o ${perfdata} -e cs_etm//u -Se -m,64K -- touch $file > /dev/null 2>&1
>  perf script -i ${perfdata} -s python:${script_path} -- \
> -	-d --stop-sample=30 2> /dev/null > ${file}
> +	-d --stop-sample=2 2> /dev/null > ${file}

[Severity: Medium]
Similarly for the userspace test, is there a risk of the script exiting
before generating any disassembly if non-branch events or interleaved CPU
events consume the strict limit of 2?

>  grep -q -E ${branch_search} ${file}
>  echo "Found userspace branches"

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260609-james-cs-context-tracking-fix-v4-0-44f9fb9e5c42@linaro.org?part=18