From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Kevin Hilman <khilman@linaro.org>,
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 15:05:39 +0100 [thread overview]
Message-ID: <1361541939.26780.63.camel@laptop> (raw)
In-Reply-To: <20130222125019.GC17948@somewhere.redhat.com>
On Fri, 2013-02-22 at 13:50 +0100, Frederic Weisbecker wrote:
> > Which is a problem how?
>
> So here is a possible scenario, CPU 0 reads a kcpustat value, and CPU
> 1 writes
> it at the same time:
>
> //Initial value of "cpustat" is 0xffffffff
> == CPU 0 == == CPU 1 ==
>
> //load low part
> mov %eax, [cpustat]
> inc [cpustat]
> //Update the high part if necessary
> jnc 1f
> inc [cpustat + 4]
> 1:
> //load high part
> mov %edx, [cpustat + 4]
>
>
> Afterward, CPU 0 will think the value is 0x1ffffffff while it's
> actually
> 0x100000000.
>
> atomic64_read() and atomic64_set() are supposed to take care of that,
> without
> even the need for _inc() or _add() parts that use LOCK.
Sure I get that, but again, why is that a problem,.. who relies on
these statistics that makes it a problem?
next prev parent reply other threads:[~2013-02-22 14:05 UTC|newest]
Thread overview: 25+ 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 ` [PATCH 1/2] cpustat: use accessor functions for get/set/add Kevin Hilman
2013-02-22 6:21 ` Viresh Kumar
2013-02-22 7:17 ` Amit Kucheria
2013-02-22 7:50 ` Viresh Kumar
2013-02-22 12:34 ` Frederic Weisbecker
2013-02-22 15:14 ` Kevin Hilman
2013-02-22 13:38 ` Frederic Weisbecker
2013-02-22 13:58 ` Peter Zijlstra
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 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 13:48 ` Peter Zijlstra
2013-02-22 13:54 ` Ingo Molnar
2013-02-22 14:04 ` Peter Zijlstra
2013-02-22 14:16 ` Ingo Molnar
2013-02-22 14:25 ` Peter Zijlstra
2013-02-22 14:05 ` Peter Zijlstra [this message]
2013-02-22 14:15 ` Frederic Weisbecker
2013-02-22 14:09 ` Peter Zijlstra
2013-02-22 14:18 ` Ingo Molnar
2013-02-22 14:21 ` Eric Dumazet
2013-02-22 14:23 ` Frederic Weisbecker
2013-02-22 19:01 ` Kevin Hilman
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