Messages in this thread |  | | | Subject | Re: [PATCH 1/5] perf: Disallow mmap() on per-task inherited events | | From | Peter Zijlstra <> | | Date | Tue, 25 May 2010 10:19:41 +0200 |
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On Tue, 2010-05-25 at 10:55 +1000, Paul Mackerras wrote: > 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.
Right, using rdpmc (and similar) should be strictly limited to strict self-monitoring.
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