From: peterz@infradead.org (Peter Zijlstra)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 0/2] cpustat: use atomic operations to read/update stats
Date: Fri, 22 Feb 2013 09:46:07 +0100 [thread overview]
Message-ID: <1361522767.26780.44.camel@laptop> (raw)
In-Reply-To: <1361512604-2720-1-git-send-email-khilman@linaro.org>
On Thu, 2013-02-21 at 21:56 -0800, Kevin Hilman wrote:
> On 64-bit platforms, reads/writes of the various cpustat fields are
> atomic due to native 64-bit loads/stores. However, on non 64-bit
> platforms, reads/writes of the cpustat fields are not atomic and could
> lead to inconsistent statistics.
Which is a problem how?
> This problem was originally reported by Frederic Weisbecker as a
> 64-bit limitation with the nsec granularity cputime accounting for
> full dynticks, but then we realized that it's a problem that's been
> around for awhile and not specific to the new cputime accounting.
>
> This series fixes this by first converting all access to the cputime
> fields to use accessor functions, and then converting the accessor
> functions to use the atomic64 functions.
Argh!! at what cost? 64bit atomics are like expensive. Wouldn't adding
a seqlock be saner?
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Kevin Hilman <khilman@linaro.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
Russell King <rmk+kernel@arm.linux.org.uk>,
Thomas Gleixner <tglx@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@kernel.org>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linaro-kernel@lists.linaro.org
Subject: Re: [PATCH 0/2] cpustat: use atomic operations to read/update stats
Date: Fri, 22 Feb 2013 09:46:07 +0100 [thread overview]
Message-ID: <1361522767.26780.44.camel@laptop> (raw)
In-Reply-To: <1361512604-2720-1-git-send-email-khilman@linaro.org>
On Thu, 2013-02-21 at 21:56 -0800, Kevin Hilman wrote:
> On 64-bit platforms, reads/writes of the various cpustat fields are
> atomic due to native 64-bit loads/stores. However, on non 64-bit
> platforms, reads/writes of the cpustat fields are not atomic and could
> lead to inconsistent statistics.
Which is a problem how?
> This problem was originally reported by Frederic Weisbecker as a
> 64-bit limitation with the nsec granularity cputime accounting for
> full dynticks, but then we realized that it's a problem that's been
> around for awhile and not specific to the new cputime accounting.
>
> This series fixes this by first converting all access to the cputime
> fields to use accessor functions, and then converting the accessor
> functions to use the atomic64 functions.
Argh!! at what cost? 64bit atomics are like expensive. Wouldn't adding
a seqlock be saner?
next prev parent reply other threads:[~2013-02-22 8:46 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-22 5:56 [PATCH 0/2] cpustat: use atomic operations to read/update stats Kevin Hilman
2013-02-22 5:56 ` Kevin Hilman
2013-02-22 5:56 ` [PATCH 1/2] cpustat: use accessor functions for get/set/add Kevin Hilman
2013-02-22 5:56 ` Kevin Hilman
2013-02-22 6:21 ` Viresh Kumar
2013-02-22 6:21 ` Viresh Kumar
2013-02-22 7:17 ` Amit Kucheria
2013-02-22 7:17 ` Amit Kucheria
2013-02-22 7:50 ` Viresh Kumar
2013-02-22 7:50 ` Viresh Kumar
2013-02-22 12:34 ` Frederic Weisbecker
2013-02-22 12:34 ` Frederic Weisbecker
2013-02-22 15:14 ` Kevin Hilman
2013-02-22 15:14 ` Kevin Hilman
2013-02-22 13:38 ` Frederic Weisbecker
2013-02-22 13:38 ` Frederic Weisbecker
2013-02-22 13:58 ` Peter Zijlstra
2013-02-22 13:58 ` Peter Zijlstra
2013-02-22 14:03 ` Frederic Weisbecker
2013-02-22 14:03 ` Frederic Weisbecker
2013-02-22 5:56 ` [PATCH 2/2] cpustat: convert to atomic operations Kevin Hilman
2013-02-22 5:56 ` Kevin Hilman
2013-02-22 8:46 ` Peter Zijlstra [this message]
2013-02-22 8:46 ` [PATCH 0/2] cpustat: use atomic operations to read/update stats Peter Zijlstra
2013-02-22 12:50 ` Frederic Weisbecker
2013-02-22 12:50 ` Frederic Weisbecker
2013-02-22 13:48 ` Peter Zijlstra
2013-02-22 13:48 ` Peter Zijlstra
2013-02-22 13:54 ` Ingo Molnar
2013-02-22 13:54 ` Ingo Molnar
2013-02-22 14:04 ` Peter Zijlstra
2013-02-22 14:04 ` Peter Zijlstra
2013-02-22 14:16 ` Ingo Molnar
2013-02-22 14:16 ` Ingo Molnar
2013-02-22 14:25 ` Peter Zijlstra
2013-02-22 14:25 ` Peter Zijlstra
2013-02-22 14:05 ` Peter Zijlstra
2013-02-22 14:05 ` Peter Zijlstra
2013-02-22 14:15 ` Frederic Weisbecker
2013-02-22 14:15 ` Frederic Weisbecker
2013-02-22 14:09 ` Peter Zijlstra
2013-02-22 14:09 ` Peter Zijlstra
2013-02-22 14:18 ` Ingo Molnar
2013-02-22 14:18 ` Ingo Molnar
2013-02-22 14:21 ` Eric Dumazet
2013-02-22 14:21 ` Eric Dumazet
2013-02-22 14:23 ` Frederic Weisbecker
2013-02-22 14:23 ` Frederic Weisbecker
2013-02-22 19:01 ` Kevin Hilman
2013-02-22 19:01 ` Kevin Hilman
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