linux-kernel - Re: [PATCH 2/2] lib kallsyms: parse using io api

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Date:   Fri, 1 May 2020 08:28:55 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 2/2] lib kallsyms: parse using io api

On Fri, May 1, 2020 at 5:23 AM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Thu, Apr 30, 2020 at 12:35:57PM -0700, Ian Rogers wrote:
> > Perf record will call kallsyms__parse 4 times during startup and process
> > megabytes of data. This changes kallsyms__parse to use the io library
> > rather than fgets to improve performance of the user code by over 8%.
> >
> > Before:
> >   Running 'internals/kallsyms-parse' benchmark:
> >   Average kallsyms__parse took: 103.988 ms (+- 0.203 ms)
> > After:
> >   Running 'internals/kallsyms-parse' benchmark:
> >   Average kallsyms__parse took: 95.571 ms (+- 0.006 ms)
> >
> > For a workload like:
> > $ perf record /bin/true
> > Run under 'perf record -e cycles:u -g' the time goes from:
> > Before
> > 30.10%     1.67%  perf     perf                [.] kallsyms__parse
> > After
> > 25.55%    20.04%  perf     perf                [.] kallsyms__parse
> > So a little under 5% of the start-up time is removed. A lot of what
> > remains is on the kernel side, but caching kallsyms within perf would
> > at least impact memory footprint.
>
> with your change I'm getting following warnings:
>
> $ sudo ./perf record -a
> Couldn't record kernel reference relocation symbol
> Symbol resolution may be skewed if relocation was used (e.g. kexec).
> Check /proc/kallsyms permission or run as root.

I'll investigate, sorry in advance for sending this out too early.

> >
> > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > ---
> >  tools/lib/api/io.h          |  3 ++
> >  tools/lib/symbol/kallsyms.c | 81 +++++++++++++++++++------------------
> >  2 files changed, 44 insertions(+), 40 deletions(-)
> >
> > diff --git a/tools/lib/api/io.h b/tools/lib/api/io.h
> > index b7e55b5f8a4a..777c20f6b604 100644
> > --- a/tools/lib/api/io.h
> > +++ b/tools/lib/api/io.h
> > @@ -7,6 +7,9 @@
> >  #ifndef __API_IO__
> >  #define __API_IO__
> >
> > +#include <stdlib.h>
> > +#include <unistd.h>
>
> was this missing?

Yes, they were getting picked up by a transitive #include in
synthesize-events.c, but given the call to read and use of size_t are
here it makes sense for the #includes to be here.

Thanks,
Ian

> jirka
>
> > +
> >  struct io {
> >       /* File descriptor being read/ */
> >       int fd;
>
> SNIP
>