linux-kernel - Re: [PATCH v3 2/2]: perf record: enable asynchronous trace writing

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Date:   Tue, 28 Aug 2018 10:50:22 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2]: perf record: enable asynchronous trace writing

On Mon, Aug 27, 2018 at 09:16:55PM +0300, Alexey Budankov wrote:
> 
> Trace file offset are linearly calculated by perf_mmap__push() code 
> for the next possible write operation, but file position is updated by 
> the kernel only in the second lseek() syscall after the loop. 
> The first lseek() syscall reads that file position for 
> the next loop iterations.
> 
> record__mmap_read_sync implements sort of a barrier between spilling 
> ready profiling data to disk.
> 
> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> ---
> Changes in v3:
> - written comments about nanosleep(0.5ms) call prior aio_suspend()
>   to cope with intrusiveness of its implementation in glibc;
> - written comments about rationale behind coping profiling data 
>   into mmap->data buffer;
> ---
>  tools/perf/builtin-record.c | 125 +++++++++++++++++++++++++++++++++++++++++---
>  tools/perf/util/mmap.c      |  36 ++++++++-----
>  tools/perf/util/mmap.h      |   2 +-
>  3 files changed, 143 insertions(+), 20 deletions(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 22ebeb92ac51..4ac61399a09a 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -53,6 +53,7 @@
>  #include <sys/mman.h>
>  #include <sys/wait.h>
>  #include <linux/time64.h>
> +#include <aio.h>
>  
>  struct switch_output {
>  	bool		 enabled;
> @@ -121,6 +122,23 @@ static int record__write(struct record *rec, void *bf, size_t size)
>  	return 0;
>  }
>  
> +static int record__aio_write(int trace_fd, struct aiocb *cblock,
> +		void *buf, size_t size, off_t off)
> +{
> +	cblock->aio_fildes = trace_fd;
> +	cblock->aio_buf    = buf;
> +	cblock->aio_nbytes = size;
> +	cblock->aio_offset = off;
> +	cblock->aio_sigevent.sigev_notify = SIGEV_NONE;
> +
> +	if (aio_write(cblock) == -1) {
> +		pr_err("failed to queue perf data, error: %m\n");
> +		return -1;
> +	}
> +
> +	return 0;
> +}
> +
>  static int process_synthesized_event(struct perf_tool *tool,
>  				     union perf_event *event,
>  				     struct perf_sample *sample __maybe_unused,
> @@ -130,12 +148,14 @@ static int process_synthesized_event(struct perf_tool *tool,
>  	return record__write(rec, event, event->header.size);
>  }
>  
> -static int record__pushfn(void *to, void *bf, size_t size)
> +static int record__pushfn(void *to, void *bf, size_t size, off_t off)
>  {
>  	struct record *rec = to;
> +	struct perf_mmap *map = bf;

the argument needs to change for record__pushfn,
now with your changes, it's no longer 'void *bf',
but 'struct perf_mmap *map'

also I'm little confused why we have '*to' and cast
it back to 'struct record', but so be it ;-)

thanks,
jirka