linux-kernel - Re: [PATCH 1/2] perf kmem: Support legacy tracepoints

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Date:   Mon, 9 Jan 2023 12:38:04 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     James Clark <james.clark@....com>
Cc:     Leo Yan <leo.yan@...aro.org>,
        Ravi Bangoria <ravi.bangoria@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] perf kmem: Support legacy tracepoints

Em Mon, Jan 09, 2023 at 03:11:47PM +0000, James Clark escreveu:
> 
> 
> On 08/01/2023 06:23, Leo Yan wrote:
> > Commit 11e9734bcb6a ("mm/slab_common: unify NUMA and UMA version of
> > tracepoints") removed tracepoints 'kmalloc_node' and
> > 'kmem_cache_alloc_node', these two tracepoints have disappeared in the
> > latest kernel, but we also need to consider the tool should be backward
> > compatible with old kernels.
> > 
> > If detects the tracepoint "kmem:kmalloc_node" is existed on a system,
> > this patch enables the legacy tracepoints, otherwise, it will ignore
> > them for the new kernels.
> > 
> > Reported-by: Ravi Bangoria <ravi.bangoria@....com>
> > Fixes: 11e9734bcb6a ("mm/slab_common: unify NUMA and UMA version of tracepoints")
> > Signed-off-by: Leo Yan <leo.yan@...aro.org>
> > ---
> >  tools/perf/builtin-kmem.c | 29 ++++++++++++++++++++++++++---
> >  1 file changed, 26 insertions(+), 3 deletions(-)
> > 
> > diff --git a/tools/perf/builtin-kmem.c b/tools/perf/builtin-kmem.c
> > index e20656c431a4..50a3df5dc18a 100644
> > --- a/tools/perf/builtin-kmem.c
> > +++ b/tools/perf/builtin-kmem.c
> > @@ -1824,6 +1824,19 @@ static int parse_line_opt(const struct option *opt __maybe_unused,
> >  	return 0;
> >  }
> >  
> > +static bool slab_legacy_tp_is_exposed(void)
> > +{
> > +	/*
> > +	 * The tracepoints "kmem:kmalloc_node" and
> > +	 * "kmem:kmem_cache_alloc_node" have been removed on the latest
> > +	 * kernel, if the tracepoint "kmem:kmalloc_node" is existed it
> > +	 * means the tool is running on an old kernel, we need to
> > +	 * rollback to support these legacy tracepoints.
> > +	 */
> > +	return IS_ERR(trace_event__tp_format("kmem", "kmalloc_node")) ?
> > +		false : true;
> > +}
> > +
> >  static int __cmd_record(int argc, const char **argv)
> >  {
> >  	const char * const record_args[] = {
> > @@ -1831,22 +1844,28 @@ static int __cmd_record(int argc, const char **argv)
> >  	};
> >  	const char * const slab_events[] = {
> >  	"-e", "kmem:kmalloc",
> > -	"-e", "kmem:kmalloc_node",
> >  	"-e", "kmem:kfree",
> >  	"-e", "kmem:kmem_cache_alloc",
> > -	"-e", "kmem:kmem_cache_alloc_node",
> >  	"-e", "kmem:kmem_cache_free",
> >  	};
> > +	const char * const slab_legacy_events[] = {
> > +	"-e", "kmem:kmalloc_node",
> > +	"-e", "kmem:kmem_cache_alloc_node",
> > +	};
> 
> Reviewed-by: James Clark <james.clark@....com>
> 
> This fixes the error with mem:kmalloc_node for me.
> 
> I was thinking that it might be best to add all events to the list
> conditionally instead of just the legacy ones. That way, the same error
> won't happen in the future. But maybe it's best to have an explicit
> error again in case the breaking change was unintentional so it's fine
> as it is I think.

Just applied this, the changes you brains stormed may come as later
patches, thanks,

- Arnaldo