From: Peter Zijlstra <peterz@infradead.org>
To: Chad Talbott <ctalbott@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Jens Axboe <jens.axboe@oracle.com>,
Divyesh Shah <dpshah@google.com>, Ingo Molnar <mingo@elte.hu>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] sched_clock: Provide local_clock() and improve documentation
Date: Fri, 28 May 2010 20:22:33 +0200 [thread overview]
Message-ID: <1275070953.1645.391.camel@laptop> (raw)
In-Reply-To: <AANLkTimbh3CsxAh9egF0etp0-uMDGb5Z9qkoltPZ6Nay@mail.gmail.com>
On Fri, 2010-05-28 at 11:11 -0700, Chad Talbott wrote:
> On Fri, May 28, 2010 at 6:13 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > + * local_clock() -- is cpu_clock() on the current cpu.
>
> Pretty sure this should read, "is cpu_clock() on *some* cpu," since
> there is no guarantee in a preemptible kernel that local_clock()
> returns on the same CPU that it was called from. The caller has to do
> the preempt protection itself.
Current cpu simply has no meaning if preemption isn't disabled. If it
is, it has and the result is useful.
Some of the local_clock() users are strictly per-cpu (and clearly have
preemption disabled), for some there simply is no better clock and
simply cope with the small incoherency in time.
next prev parent reply other threads:[~2010-05-28 18:22 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-24 3:03 BUG: using smp_processor_id() in preemptible [00000000] code: icedove-bin/5449 Piotr Hosowicz
2010-05-24 17:22 ` Piotr Hosowicz
2010-05-25 8:50 ` Peter Zijlstra
2010-05-25 9:42 ` Piotr Hosowicz
2010-05-25 9:45 ` Peter Zijlstra
2010-05-25 9:43 ` Ingo Molnar
2010-05-25 9:47 ` Peter Zijlstra
2010-05-25 9:51 ` Peter Zijlstra
2010-05-25 9:57 ` Piotr Hosowicz
2010-05-25 10:00 ` Peter Zijlstra
2010-05-25 10:05 ` Piotr Hosowicz
2010-05-25 10:29 ` Piotr Hosowicz
2010-05-25 14:13 ` Piotr Hosowicz
2010-05-25 14:34 ` Piotr Hosowicz
2010-05-25 14:36 ` Peter Zijlstra
2010-05-25 14:48 ` Piotr Hosowicz
2010-05-25 16:15 ` Peter Zijlstra
2010-05-25 16:47 ` Piotr Hosowicz
2010-05-26 2:06 ` Piotr Hosowicz
2010-05-26 2:51 ` Piotr Hosowicz
2010-05-25 18:07 ` Divyesh Shah
2010-05-25 18:15 ` Piotr Hosowicz
2010-05-25 21:35 ` Peter Zijlstra
2010-05-26 23:02 ` Andrew Morton
2010-05-27 6:46 ` Peter Zijlstra
2010-05-27 6:51 ` Andrew Morton
[not found] ` <1274945751.27810.3765.camel@twins>
[not found] ` <20100527113340.d4afb8fc.akpm@linux-foundation.org>
2010-05-28 13:13 ` [PATCH] sched_clock: Provide local_clock() and improve documentation Peter Zijlstra
2010-05-28 13:42 ` Johannes Stezenbach
2010-05-28 15:08 ` Peter Zijlstra
2010-05-28 14:15 ` Piotr Hosowicz
2010-05-28 14:22 ` Piotr Hosowicz
2010-05-28 18:11 ` Chad Talbott
2010-05-28 18:22 ` Peter Zijlstra [this message]
2010-06-09 10:13 ` [tip:sched/core] sched_clock: Add local_clock() API " tip-bot for Peter Zijlstra
2010-06-01 6:41 ` BUG: using smp_processor_id() in preemptible [00000000] code: icedove-bin/5449 Ingo Molnar
2010-06-01 6:47 ` Jens Axboe
2010-06-01 6:55 ` Ingo Molnar
2010-06-01 7:53 ` Jens Axboe
2010-06-12 1:54 ` Divyesh Shah
2010-06-12 9:42 ` Peter Zijlstra
2010-06-02 11:16 ` blkiocg_update_io_add_stats(): INFO: trying to register non-static key Ingo Molnar
2010-06-02 13:04 ` Jens Axboe
2010-06-11 1:33 ` Divyesh Shah
2010-06-11 7:15 ` Peter Zijlstra
2010-06-11 8:34 ` Jens Axboe
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