Re: [PATCH v3] perf trace: Introduce --show-cpu option to display cpu id

[sashiko-bot@kernel.org]

Sashiko AI review found 1 potential issue(s):
- [Medium] The `--show-cpu` option fails to print the CPU ID for interrupted system call entries, resulting in lost information and broken columnar alignment.
--

commit f837c4ea902d9b8f1e88b211cf0a2320cd3c7a26
Author: Aaron Tomlin <atomlin@atomlin.com>
perf trace: Introduce --show-cpu option to display cpu id

This commit introduces the --show-cpu option for perf trace. It extracts 
the CPU from the perf sample and prints it alongside the timestamp to 
better trace system-wide workloads.

> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index 311d9da9896a41..820b0a304ff90f 100644
> --- a/tools/perf/builtin-trace.c
> +++ b/tools/perf/builtin-trace.c

[ ... ]

> @@ -2704,7 +2729,9 @@ static int trace__printf_interrupted_entry(struct trace *trace)
>  	if (!ttrace->entry_pending)
>  		return 0;
>  
> -	printed  = trace__fprintf_entry_head(trace, trace->current, 0, false, ttrace->entry_time, trace->output);
> +	printed = trace__fprintf_entry_head(trace, trace->current, 0, false,
> +					    ttrace->entry_time, (u32)-1,
> +					    trace->output);

When a system call entry is processed in trace__sys_enter(), it is often
buffered (ttrace->entry_pending = true) so it can be combined with its
exit event on a single line. Does hardcoding (u32)-1 here cause the CPU ID
to be lost when a pending entry is interrupted?

Since trace__fprintf_entry_head() skips printing the CPU ID entirely when
the cpu is (u32)-1, it appears this will omit the CPU column for interrupted
entries (which print with " ..."). Could this break the columnar alignment of
the output?

Would it be better to extend struct thread_trace to store the cpu ID from the
sample during trace__sys_enter(), so it can be accurately printed when the
entry is flushed here?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260423194032.134416-1-atomlin@atomlin.com?part=1