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Date: Tue, 15 Oct 2013 09:30:41 -0600
From: David Ahern <dsahern@gmail.com>
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To: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>
CC: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        linux-kernel@vger.kernel.org, Frederic Weisbecker <fweisbec@gmail.com>,
        Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
        Mike Galbraith <efault@gmx.de>, Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH 3/3] perf record: mmap output file
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On 10/15/13 9:27 AM, Ingo Molnar wrote:
>
> * Peter Zijlstra <peterz@infradead.org> wrote:
>
>> On Tue, Oct 15, 2013 at 11:32:45AM -0300, Arnaldo Carvalho de Melo wrote:
>>
>>> Jiri and PeterZ probaby will have comments here... ;-) :-)
>>
>> The only complication with splice is the vmalloc support; other than
>> that it should be fairly straight fwd.
>
> In the initial version we could skip splice support for vmalloc
> ring-buffer, to keep things simple.
>
> Wanna send a patch for people to try? Looks like there's real interest in
> speeding up perf record as much as possible!

My second -- and more important -- concern about splice has been dropped 
from this path:

"splice is also a system call and it would have to be invoked for each 
mmap each trip through the loop -- just like write() does today -- so it 
does not solve the feedback loop problem. "

Am I missing something on how splice works?

David