From: Paul Mackerras <paulus@samba.org>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>,
Arnaldo Carvalho de Melo <acme@infradead.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/5] perf: Disallow mmap() on per-task inherited events
Date: Tue, 25 May 2010 10:55:28 +1000 [thread overview]
Message-ID: <20100525005528.GB30395@drongo> (raw)
In-Reply-To: <20100518133725.885757039@chello.nl>
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.
next prev parent reply other threads:[~2010-05-25 1:07 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-18 13:32 [PATCH 0/5] Optimize perf ring-buffer Peter Zijlstra
2010-05-18 13:32 ` [PATCH 1/5] perf: Disallow mmap() on per-task inherited events Peter Zijlstra
2010-05-19 7:19 ` Frederic Weisbecker
2010-05-25 0:55 ` Paul Mackerras [this message]
2010-05-25 8:19 ` Peter Zijlstra
2010-05-18 13:33 ` [PATCH 2/5] perf: Remove IRQ-disable from the perf_output path Peter Zijlstra
2010-05-18 13:33 ` [PATCH 3/5] perf: Convert the perf output buffer to local_t Peter Zijlstra
2010-05-18 13:33 ` [PATCH 4/5] perf: Avoid local_xchg Peter Zijlstra
2010-05-18 13:33 ` [RFC PATCH 5/5] perf: Implement perf_output_addr() Peter Zijlstra
2010-05-18 14:09 ` Peter Zijlstra
2010-05-19 7:21 ` Frederic Weisbecker
2010-05-19 7:58 ` Peter Zijlstra
2010-05-19 9:03 ` Frederic Weisbecker
2010-05-19 14:47 ` Steven Rostedt
2010-05-19 15:05 ` Peter Zijlstra
2010-05-19 15:38 ` Steven Rostedt
2010-05-19 15:50 ` Peter Zijlstra
2010-05-19 16:08 ` Steven Rostedt
2010-05-19 16:15 ` Peter Zijlstra
2010-05-19 16:27 ` Steven Rostedt
2010-05-19 16:34 ` Peter Zijlstra
2010-05-19 7:14 ` [PATCH 0/5] Optimize perf ring-buffer Frederic Weisbecker
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