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From: Ingo Molnar <mingo@kernel.org>
To: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: linux-kernel@vger.kernel.org,
	Adrian Hunter <adrian.hunter@intel.com>,
	David Ahern <dsahern@gmail.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Ingo Molnar <mingo@redhat.com>, Jiri Olsa <jolsa@redhat.com>,
	Mike Galbraith <efault@gmx.de>, Namhyung Kim <namhyung@gmail.com>,
	Paul Mackerras <paulus@samba.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Stephane Eranian <eranian@google.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Namhyung Kim <namhyung@kernel.org>
Subject: Re: [PATCH 10/10] perf record: Add an option to force per-cpu mmaps
Date: Fri, 15 Nov 2013 07:06:43 +0100	[thread overview]
Message-ID: <20131115060643.GA9237@gmail.com> (raw)
In-Reply-To: <1384460715-23198-11-git-send-email-acme@infradead.org>


* Arnaldo Carvalho de Melo <acme@infradead.org> wrote:

> +--force-per-cpu::
> + Force the use of per-cpu mmaps.  By default, when tasks are specified (i.e. -p,
> + -t or -u options) per-thread mmaps are created.  This option overrides that and
> + forces per-cpu mmaps.  A side-effect of that is that inheritance is
> + automatically enabled.  Add the -i option also to disable inheritance.

So I still haven't seen an explanation why it's called 'force' 
anything. AFAICS nothing is 'forced' really, this is simply another 
trace-ringbuffer setup method, right?

And I also raised why this shouldn't be the default event tracing 
method instead of a weird config option. Per-cpu tracing is cache 
compact, it is easier to size properly and in general it is pretty 
easy to think about. (It also has less of the TSC timestamp ordering 
problems as per thread tracing, at least in theory.)

Is there something that makes per cpu tracing undesirable as the 
default?

Thanks,

	Ingo

  reply	other threads:[~2013-11-15  6:06 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-11-14 20:25 [GIT PULL 00/10] perf/core improvements and fixes Arnaldo Carvalho de Melo
2013-11-14 20:25 ` [PATCH 01/10] perf trace: Tweak summary output Arnaldo Carvalho de Melo
2013-11-14 20:25 ` [PATCH 02/10] perf tools: Remove trivial extra semincolon Arnaldo Carvalho de Melo
2013-11-14 20:25 ` [PATCH 03/10] perf top: Add missing newline if the 'uid' is invalid Arnaldo Carvalho de Melo
2013-11-14 20:25 ` [PATCH 04/10] perf tools: Synthesize anon MMAP records again Arnaldo Carvalho de Melo
2013-11-14 20:25 ` [PATCH 05/10] perf tools: Use perf_evlist__{first,last}, perf_evsel__next Arnaldo Carvalho de Melo
2013-11-14 20:25 ` [PATCH 06/10] perf evsel: Introduce perf_evsel__prev() method Arnaldo Carvalho de Melo
2013-11-14 20:25 ` [PATCH 07/10] perf symbols: Limit max callchain using max_stack on DWARF unwinding too Arnaldo Carvalho de Melo
2013-11-14 20:25 ` [PATCH 08/10] perf ui browser: Fix segfault caused by off by one handling END key Arnaldo Carvalho de Melo
2013-11-14 20:25 ` [PATCH 09/10] perf probe: Add '--demangle'/'--no-demangle' Arnaldo Carvalho de Melo
2013-11-14 20:25 ` [PATCH 10/10] perf record: Add an option to force per-cpu mmaps Arnaldo Carvalho de Melo
2013-11-15  6:06   ` Ingo Molnar [this message]
2013-11-15 11:00     ` Adrian Hunter
2013-11-15 11:10       ` Ingo Molnar
2013-11-15 11:27         ` Adrian Hunter
2013-11-15 11:56           ` Ingo Molnar
2013-11-15 12:03             ` Peter Zijlstra
2013-11-15 12:05               ` Ingo Molnar
2013-11-15 12:30                 ` Peter Zijlstra
2013-11-15 12:33                 ` Adrian Hunter
2013-11-15 12:52               ` Adrian Hunter
2013-11-15 12:53                 ` Peter Zijlstra
2013-11-15 13:52       ` [PATCH V2] perf record: Make per-cpu mmaps the default Adrian Hunter
2013-11-30 12:50         ` [tip:perf/core] " tip-bot for Adrian Hunter
2013-11-15  6:38 ` [GIT PULL 00/10] perf/core improvements and fixes Ingo Molnar

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