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

Jiri Olsa
2020-05-01T12:23:57Z

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@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?

jirka

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

SNIP