linux-kernel - Re: [PATCH v2 0/4] perf lock contention: Symbolize locks using slab cache names

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Message-ID: <Z1xqdFB0210tP3RY@google.com>
Date: Fri, 13 Dec 2024 09:10:12 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
	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,
	Andrii Nakryiko <andrii@...nel.org>, Song Liu <song@...nel.org>,
	bpf@...r.kernel.org, Stephane Eranian <eranian@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v2 0/4] perf lock contention: Symbolize locks using slab
 cache names

Hello,

On Mon, Nov 18, 2024 at 10:35:43AM -0800, Namhyung Kim wrote:
> On Mon, Nov 11, 2024 at 11:46:37AM -0800, Ian Rogers wrote:
> > On Thu, Nov 7, 2024 at 10:15 PM Namhyung Kim <namhyung@...nel.org> wrote:
> > >
> > > Hello,
> > >
> > > This is to support symbolization of dynamic locks using slab
> > > allocator's metadata.  The kernel support is in the bpf-next tree now.
> > >
> > > It provides the new "kmem_cache" BPF iterator and "bpf_get_kmem_cache"
> > > kfunc to get the information from an address.  The feature detection is
> > > done using BTF type info and it won't have any effect on old kernels.
> > >
> > > v2 changes)
> > >
> > >  * don't use libbpf_get_error()  (Andrii)
> > >
> > > v1) https://lore.kernel.org/linux-perf-users/20241105172635.2463800-1-namhyung@kernel.org
> > >
> > > With this change, it can show locks in a slab object like below.  I
> > > added "&" sign to distinguish them from global locks.
> > 
> > I know the & is intentional but I worry it could later complicate
> > parsing of filters. Perhaps @ is a viable alternative. Other than
> > that:
> > 
> > Acked-by: Ian Rogers <irogers@...gle.com>
> 
> Thanks for the review!
> 
> I don't think it clashes with BPF sample filters which works on sample
> data generated from a perf_event.  Technically this command doesn't use
> perf_event and just attaches the BPF program to tracepoint directly.
> 
> Also sample filters don't use '&' symbol in the syntax as of now. :)

Can we merge this series if no more feedback?

About the build issue, I think it's transient and it's not the default
to build with generated vmlinux.h.  We could disable the generation but
it might be better to keep it to test other issues.  Anyway, it can be
done independently.

Thanks,
Namhyung