linux-kernel - Re: [PATCH v11 2/3]: perf record: enable asynchronous trace writing

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Date:   Mon, 8 Oct 2018 14:53:10 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.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 v11 2/3]: perf record: enable asynchronous trace writing

On Mon, Oct 08, 2018 at 03:24:31PM +0300, Alexey Budankov wrote:
> Hi,
> 
> On 08.10.2018 13:52, Jiri Olsa wrote:
> > On Mon, Oct 08, 2018 at 09:17:11AM +0300, Alexey Budankov wrote:
> <SNIP>
> >> +#ifdef HAVE_AIO_SUPPORT
> >> +	off = lseek(trace_fd, 0, SEEK_CUR);
> >> +#endif
> > 
> > I'm still little puzzled why we need to do this,
> > when the aio write takes the offset value, but
> 
> pwrite() syscall [1] which is the base for aio_write() doesn't 
> advance file pos value so it requires to be calculated and 
> updated by callers of aio_write() API.

ok, so aio_write does not need the offset to be updated,
who needs it then?

jirka