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

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Message-ID: <20200501122345.GA1810115@krava>
Date:   Fri, 1 May 2020 14:23:45 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Ian Rogers <irogers@...gle.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>,
        linux-kernel@...r.kernel.org, Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 2/2] lib kallsyms: parse using io api

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.

> 
> 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?

jirka

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

SNIP