Messages in this thread | | | Date | Tue, 25 May 2010 10:55:28 +1000 | From | Paul Mackerras <> | Subject | Re: [PATCH 1/5] perf: Disallow mmap() on per-task inherited events |
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On Tue, May 18, 2010 at 03:32:59PM +0200, Peter Zijlstra wrote:
> Since we now have working per-task-per-cpu events for a while, > disallow mmap() on per-task inherited events. Those things were > a performance problem anyway, and doing away with it allows > us to optimize the buffer somewhat by assuming there is only a single > writer.
This also disallows user-space access to hardware counter for this event -- which is arguably OK, since doing the userspace read would give a different answer to read() on the event fd, as the read() sums up all the child counters for us. Nevertheless, I think this side-effect is worth mentioning.
Paul.
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