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

Ian Rogers
2020-05-01T15:29:10Z

On Fri, May 1, 2020 at 5:23 AM Jiri Olsa <jolsa@redhat.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@google.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
>