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SubjectRe: [PATCH 4/5] perf record: mmap output file - v5
On 11/13/13, 4:50 AM, Ingo Molnar wrote:
>>>> one option here is not allow page faults and system wide system
>>>> calls. system wide tracing needs mmap; page faults for a task can
>>>> use write(). I left that option in case something like this came up.
>>> So maybe splice() sounds like the right long term solution after all?
>>> :-/
>> Right until you put a tracepoint (kprobe) somewhere in whatever function
>> is used to transfer a single page into/from a splice pipe.
> That ought to be a far less common occurance than tracing page faults
> though.
>> You can always screw yourself over using this stuff, no exceptions.
> Granted, as the many notrace markings demonstrate this stuff really wants
> to observe itself observing itself all the time! :)

perf can have options for output -- write(), mmap(), splice() -- and
some logic of when not to use it:

1. don't use write for system wide tracing

2. don't use mmap for page fault tracing

3. don't use splice for .... (need a splice implementation)

and allow the user to override.


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