Re: [PATCH] perf data: Allow to use stdio functions for pipe mode

[Jiri Olsa <jolsa@redhat.com>]

On Wed, Oct 28, 2020 at 05:56:32PM +0900, Namhyung Kim wrote:
> When perf data is in a pipe, it reads each event separately using
> read(2) syscall.  This is a huge performance bottleneck when
> processing large data like in perf inject.  Also perf inject needs to
> use write(2) syscall for the output.
> 
> So convert it to use buffer I/O functions in stdio library for pipe
> data.  This makes inject-build-id bench time drops from 20ms to 8ms.
> 
>   $ perf bench internals inject-build-id
>   # Running 'internals/inject-build-id' benchmark:
>     Average build-id injection took: 8.074 msec (+- 0.013 msec)
>     Average time per event: 0.792 usec (+- 0.001 usec)
>     Average memory usage: 8328 KB (+- 0 KB)
>     Average build-id-all injection took: 5.490 msec (+- 0.008 msec)
>     Average time per event: 0.538 usec (+- 0.001 usec)
>     Average memory usage: 7563 KB (+- 0 KB)
> 
> This patch enables it just for perf inject when used with pipe (it's a
> default behavior).  Maybe we could do it for perf record and/or report
> later..
> 
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
>  tools/perf/builtin-inject.c |  2 ++
>  tools/perf/util/data.c      | 36 +++++++++++++++++++++++++++++++++---
>  tools/perf/util/data.h      | 11 ++++++++++-
>  tools/perf/util/header.c    |  8 ++++----
>  tools/perf/util/session.c   |  7 ++++---
>  5 files changed, 53 insertions(+), 11 deletions(-)
> 
> diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
> index 452a75fe68e5..14d6c88fed76 100644
> --- a/tools/perf/builtin-inject.c
> +++ b/tools/perf/builtin-inject.c
> @@ -853,10 +853,12 @@ int cmd_inject(int argc, const char **argv)
>  		.output = {
>  			.path = "-",
>  			.mode = PERF_DATA_MODE_WRITE,
> +			.use_stdio = true,
>  		},
>  	};
>  	struct perf_data data = {
>  		.mode = PERF_DATA_MODE_READ,
> +		.use_stdio = true,
>  	};
>  	int ret;
>  
> diff --git a/tools/perf/util/data.c b/tools/perf/util/data.c
> index c47aa34fdc0a..47b5a4b50ca5 100644
> --- a/tools/perf/util/data.c
> +++ b/tools/perf/util/data.c
> @@ -174,8 +174,16 @@ static bool check_pipe(struct perf_data *data)
>  			is_pipe = true;
>  	}
>  
> -	if (is_pipe)
> -		data->file.fd = fd;
> +	if (is_pipe) {
> +		if (data->use_stdio) {
> +			const char *mode;
> +
> +			mode = perf_data__is_read(data) ? "r" : "w";
> +			data->file.fptr = fdopen(fd, mode);

I guess fdopen should never fail right? but I think we should
add BUG_ON(data->file.fptr == NULL) or something

other than this the change looks good, I can see the speedup
in bench as well

jirka