From: David Ahern <dsahern@gmail.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
linux-kernel@vger.kernel.org,
Frederic Weisbecker <fweisbec@gmail.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Mike Galbraith <efault@gmx.de>,
Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH 3/3] perf record: mmap output file
Date: Tue, 15 Oct 2013 10:16:44 -0600 [thread overview]
Message-ID: <525D6A6C.3090208@gmail.com> (raw)
In-Reply-To: <20131015160646.GC16003@gmail.com>
On 10/15/13 10:06 AM, Ingo Molnar wrote:
> splice() is very fast and should be able to process a lot of pages in one
> go, so the feedback loop should be pretty weak. mmap() triggers kernel
> code as well, every time we run out of the 64 MB window we got to remap
> it, right?
Yes, 1 mmap, 1 munmap for every 64MB. Compare to the write() case which
calls write() for each mmap each time through the mmap_read loop.
I am conjecturing that splice would follow the write model in the sense
of a ring buffer has N bytes, call splice to copy the data from the ring
buffer to the file. So, splice saves on the memcpy, but not the syscalls.
David
next prev parent reply other threads:[~2013-10-15 16:16 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-09 3:26 [PATCH 0/3] perf trace enhancements David Ahern
2013-10-09 3:26 ` [PATCH 1/3] perf util: Add findnew method to intlist - v2 David Ahern
2013-10-15 5:32 ` [tip:perf/core] perf util: Add findnew method to intlist tip-bot for David Ahern
2013-10-09 3:26 ` [PATCH 2/3] perf trace: Add summary option to dump syscall statistics David Ahern
2013-10-09 13:16 ` Jiri Olsa
2013-10-15 5:32 ` [tip:perf/core] " tip-bot for David Ahern
2013-10-09 3:26 ` [PATCH 3/3] perf record: mmap output file David Ahern
2013-10-09 5:59 ` Ingo Molnar
2013-10-15 14:04 ` David Ahern
2013-10-15 14:32 ` Arnaldo Carvalho de Melo
2013-10-15 14:38 ` Peter Zijlstra
2013-10-15 15:27 ` Ingo Molnar
2013-10-15 15:29 ` Peter Zijlstra
2013-10-15 15:30 ` David Ahern
2013-10-15 16:06 ` Ingo Molnar
2013-10-15 16:16 ` David Ahern [this message]
2013-10-16 7:11 ` Ingo Molnar
2013-10-15 16:37 ` Peter Zijlstra
2013-10-09 7:14 ` Mike Galbraith
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