From: Paul Mackerras <paulus@samba.org>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>,
linux-kernel@vger.kernel.org, Mike Galbraith <efault@gmx.de>,
Arjan van de Ven <arjan@infradead.org>,
Wu Fengguang <fengguang.wu@intel.com>
Subject: Re: [PATCH 5/6] perf_counter: kerneltop: mmap_pages argument
Date: Thu, 26 Mar 2009 13:22:27 +1100 [thread overview]
Message-ID: <18890.59107.116394.771297@drongo.ozlabs.ibm.com> (raw)
In-Reply-To: <1237984033.7972.865.camel@twins>
Peter Zijlstra writes:
> One possible solution is making the control page writable and writing
> the userspace read position to it, then the kernel can, on
> perf_output_begin() detect the overflow and count the number of
> overwritten events.
>
> This overflow count could then be published back into the control page.
We could in principle have many different processes mmapping the same
counter and reading the ring buffer, couldn't we? So which process
gets to put its read position in the control page?
> TBH I'm not much of a fan, making all these pages writable just opens a
> whole can of worms, and that accurate overflow tracking will put more
> code in the output path.
I agree.
Paul.
next prev parent reply other threads:[~2009-03-26 2:43 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-25 11:30 [PATCH 0/6] perf_counter: new output ABI Peter Zijlstra
2009-03-25 11:30 ` [PATCH 1/6] perf_counter: more elaborate write API Peter Zijlstra
2009-03-25 12:06 ` [tip:perfcounters/core] " Peter Zijlstra
2009-03-25 11:30 ` [PATCH 2/6] perf_counter: output objects Peter Zijlstra
2009-03-25 12:06 ` [tip:perfcounters/core] " Peter Zijlstra
2009-03-25 11:30 ` [PATCH 3/6] perf_counter: sanity check on the output API Peter Zijlstra
2009-03-25 12:06 ` [tip:perfcounters/core] " Peter Zijlstra
2009-03-25 11:30 ` [PATCH 4/6] perf_counter: optionally provide the pid/tid of the sampled task Peter Zijlstra
2009-03-25 12:06 ` [tip:perfcounters/core] " Peter Zijlstra
2009-03-25 11:30 ` [PATCH 5/6] perf_counter: kerneltop: mmap_pages argument Peter Zijlstra
2009-03-25 12:07 ` [tip:perfcounters/core] " Peter Zijlstra
2009-03-25 12:18 ` [PATCH 5/6] " Ingo Molnar
2009-03-25 12:27 ` Peter Zijlstra
2009-03-25 12:35 ` Ingo Molnar
2009-03-25 12:41 ` Peter Zijlstra
2009-03-25 12:54 ` Ingo Molnar
2009-03-25 12:57 ` Peter Zijlstra
2009-03-25 14:52 ` Peter Zijlstra
2009-03-25 17:16 ` Ingo Molnar
2009-03-25 21:18 ` Peter Zijlstra
2009-03-26 2:22 ` Paul Mackerras [this message]
2009-03-25 11:30 ` [PATCH 6/6] perf_counter: kerneltop: output event support Peter Zijlstra
2009-03-25 12:07 ` [tip:perfcounters/core] " Peter Zijlstra
2009-04-04 0:21 ` [PATCH 6/6] " Corey Ashford
2009-04-04 12:17 ` Peter Zijlstra
2009-04-04 18:10 ` Corey Ashford
2009-03-25 12:05 ` [PATCH 0/6] perf_counter: new output ABI Ingo Molnar
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