linux-kernel - Re: [PATCH] perf report: Do not process non-JIT BPF ksymbol events

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Message-ID: <CAPhsuW6TCv=F69gdZvdzw4wQgnHepVGW_+6gxpmXJu7RYEL9xQ@mail.gmail.com>
Date: Wed, 5 Mar 2025 20:09:05 -0800
From: Song Liu <song@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>, Ian Rogers <irogers@...gle.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>, 
	linux-perf-users@...r.kernel.org, bpf@...r.kernel.org, 
	Kevin Nomura <nomurak@...gle.com>
Subject: Re: [PATCH] perf report: Do not process non-JIT BPF ksymbol events

On Wed, Mar 5, 2025 at 3:28 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> The length of PERF_RECORD_KSYMBOL for BPF is a size of JITed code so
> it'd be 0 when it's not JITed.  The ksymbol is needed to symbolize the
> code when it gets samples in the region but non-JITed code cannot get
> samples.  Thus it'd be ok to ignore them.
>
> Actually it caused a performance issue in the perf tools on old ARM
> kernels where it can refuse to JIT some BPF codes.  It ended up
> splitting the existing kernel map (kallsyms).  And later lookup for a
> kernel symbol would create a new kernel map from kallsyms and then
> split it again and again. :(
>
> Probably there's a bug in the kernel map/symbol handling in perf tools.
> But I think we need to fix this anyway.
>
> Reported-by: Kevin Nomura <nomurak@...gle.com>
> Cc: Song Liu <song@...nel.org>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>

Acked-by: Song Liu <song@...nel.org>