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SubjectRe: [PATCH 3/3] perf record: mmap output file
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



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