From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: David Ahern <dsahern@gmail.com>,
Namhyung Kim <namhyung@kernel.org>,
Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
linux-kernel@vger.kernel.org, jolsa@redhat.com,
Frederic Weisbecker <fweisbec@gmail.com>,
Mike Galbraith <efault@gmx.de>,
Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH 4/5] perf record: mmap output file - v5
Date: Tue, 19 Nov 2013 12:48:10 +0100 [thread overview]
Message-ID: <20131119114810.GK3866@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20131119065835.GB32367@gmail.com>
On Tue, Nov 19, 2013 at 07:58:35AM +0100, Ingo Molnar wrote:
>
> * David Ahern <dsahern@gmail.com> wrote:
>
> > This is mmap'ed output, not the ring buffers or its stack. As the
> > output file grows, new pages are needed and those are allocated on
> > access via page faults. The ftruncate only extends the file size, it
> > does not allocate pages at that time.
>
> Hm, doesn't MAP_POPULATE prefault pages in this case as well?
> Prefaulting would avoid the most obvious page fault driven feedback
> loops and it would probably be faster as well, because it avoids all
> the pagefaults ...
MAP_POPULATE does indeed seem to write pre-fault for writable maps
(mm/mlock.c:__mlock_vma_pages_range).
And that does indeed seem to side-step the perf sw pagefault event, but
that is arguably a perf bug.
If we were to fix this, MAP_POPULATE would simply generate a metric ton
of events, we'd have to write out with yet more MAP_POPULATE.
next prev parent reply other threads:[~2013-11-19 11:48 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-12 14:46 [PATCH 0/5] " David Ahern
2013-11-12 14:46 ` [PATCH 1/5] perf record: Fix segfault with --no-mmap-pages David Ahern
2013-11-12 21:57 ` [tip:perf/urgent] " tip-bot for David Ahern
2013-11-12 14:46 ` [PATCH 2/5] perf tool: Round mmap pages to power 2 - v2 David Ahern
2013-11-12 21:57 ` [tip:perf/urgent] perf evlist: " tip-bot for David Ahern
2013-11-12 14:46 ` [PATCH 3/5] perf tool: Refactor mmap_pages parsing David Ahern
2013-11-12 21:57 ` [tip:perf/urgent] perf evlist: " tip-bot for David Ahern
2013-11-12 14:46 ` [PATCH 4/5] perf record: mmap output file - v5 David Ahern
2013-11-12 14:57 ` Peter Zijlstra
2013-11-12 15:07 ` Arnaldo Carvalho de Melo
2013-11-12 15:19 ` Peter Zijlstra
2013-11-12 15:36 ` David Ahern
2013-11-12 21:11 ` Ingo Molnar
2013-11-13 11:34 ` Peter Zijlstra
2013-11-13 11:50 ` Ingo Molnar
2013-11-13 12:16 ` Peter Zijlstra
2013-11-13 14:29 ` David Ahern
2013-11-15 16:41 ` David Ahern
2013-11-18 9:01 ` Peter Zijlstra
2013-11-18 9:40 ` Ingo Molnar
2013-11-19 0:24 ` Namhyung Kim
2013-11-19 0:34 ` David Ahern
2013-11-19 1:48 ` Namhyung Kim
2013-11-19 2:02 ` Namhyung Kim
2013-11-19 2:13 ` Namhyung Kim
2013-11-19 2:17 ` David Ahern
2013-11-19 2:30 ` Namhyung Kim
2013-11-19 2:33 ` David Ahern
2013-11-19 2:36 ` Namhyung Kim
2013-11-19 6:58 ` Ingo Molnar
2013-11-19 11:48 ` Peter Zijlstra [this message]
2013-11-19 11:49 ` Peter Zijlstra
2013-11-19 13:13 ` Ingo Molnar
2013-11-19 13:45 ` Peter Zijlstra
2013-11-19 15:31 ` Ingo Molnar
2013-11-19 16:09 ` David Ahern
2013-11-19 16:14 ` Ingo Molnar
2013-11-19 12:08 ` Peter Zijlstra
2013-11-19 6:54 ` Ingo Molnar
2013-11-12 14:46 ` [PATCH 5/5] perf record: Handle out of space failures writing data with mmap David Ahern
2013-11-12 21:19 ` Ingo Molnar
2013-11-13 14:33 ` David Ahern
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