From: "H. Peter Anvin" <hpa@zytor.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Dominique Toupin <dominique.toupin@ericsson.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Steven Rostedt <rostedt@goodmis.org>,
Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Frederic Weisbecker <fweisbec@gmail.com>,
"2nddept-manager@sdl.hitachi.co.jp"
<2nddept-manager@sdl.hitachi.co.jp>
Subject: Re: [RFC][PATCH 0/4] ftrace: Use -mfentry when supported (this is for x86_64 right now)
Date: Fri, 18 Feb 2011 14:45:19 -0800 [thread overview]
Message-ID: <4D5EF67F.20007@zytor.com> (raw)
In-Reply-To: <20110218223902.GR5818@one.firstfloor.org>
On 02/18/2011 02:39 PM, Andi Kleen wrote:
> On Fri, Feb 18, 2011 at 03:10:18PM -0500, Dominique Toupin wrote:
>>
>> My understanding is stop_machine will stop all processors for many ms.
>
> I haven't measured it recently, but as long as the callback inside stop
> machine is short it definitely shouldn't be "many ms". The latency
> is bound by how long each CPU needs to answer to an interrupt, so if
> you have some code that disables interrupts for a long time it will take
> long -- but then your realtime response will be already bad.
>
> The interrupts are also done in parallel, so the interrupt latencies
> don't add up.
>
> If all the CPUs answer in a reasonable time it's still not a cheap
> operation, but nothing that takes "many ms". Most likely it's fine
> for most soft real time purposes.
>
We should also be able to use the breakpoint hack to avoid holding all
the CPUs. They still need to be interrupted, but that skips the
rendezvous operation.
-hpa
next prev parent reply other threads:[~2011-02-18 22:46 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-09 20:02 [RFC][PATCH 0/4] ftrace: Use -mfentry when supported (this is for x86_64 right now) Steven Rostedt
2011-02-09 20:02 ` [RFC][PATCH 1/4] ftrace: Make recordmcount.c handle __fentry__ Steven Rostedt
2011-02-09 20:02 ` [RFC][PATCH 2/4] ftrace: Add -mfentry to Makefile on function tracer Steven Rostedt
2011-02-09 20:28 ` Steven Rostedt
2011-02-09 21:22 ` H. Peter Anvin
2011-02-09 20:02 ` [RFC][PATCH 3/4] ftrace: Do not test frame pointers if -mfentry is used Steven Rostedt
2011-02-09 20:02 ` [RFC][PATCH 4/4] ftrace/x86: Add support for -mfentry to x86_64 Steven Rostedt
2011-02-10 2:38 ` [RFC][PATCH 0/4] ftrace: Use -mfentry when supported (this is for x86_64 right now) Masami Hiramatsu
2011-02-17 12:37 ` Masami Hiramatsu
2011-02-17 13:18 ` Steven Rostedt
2011-02-17 15:34 ` Masami Hiramatsu
2011-02-17 15:46 ` Steven Rostedt
2011-02-17 16:07 ` Masami Hiramatsu
2011-02-17 20:11 ` Steven Rostedt
2011-02-18 11:45 ` Masami Hiramatsu
2011-02-18 15:07 ` Steven Rostedt
2011-02-18 15:19 ` Mathieu Desnoyers
2011-02-18 20:10 ` Dominique Toupin
2011-02-18 20:36 ` Steven Rostedt
2011-02-18 21:45 ` Dominique Toupin
2011-02-18 22:39 ` Andi Kleen
2011-02-18 22:45 ` H. Peter Anvin [this message]
2011-02-18 23:02 ` Steven Rostedt
2011-02-19 5:07 ` Masami Hiramatsu
2011-02-19 5:10 ` hpas
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