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From: mingo@kernel.org (Ingo Molnar)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 0/2] cpustat: use atomic operations to read/update stats
Date: Fri, 22 Feb 2013 15:18:10 +0100	[thread overview]
Message-ID: <20130222141810.GB9606@gmail.com> (raw)
In-Reply-To: <1361542150.26780.64.camel@laptop>


* Peter Zijlstra <peterz@infradead.org> wrote:

> On Fri, 2013-02-22 at 13:50 +0100, Frederic Weisbecker wrote:
> > > Argh!! at what cost? 64bit atomics are like expensive. Wouldn't
> > adding
> > > a seqlock be saner?
> > 
> > Not sure. This requires a spinlock in the write side which is called
> > from
> > fast path like the timer interrupt.
> 
> A single spinlock is _way_ cheaper than a ton of cmpxchg8b()s 
> to update a few variables.

Every cmpxchg8b() will be roughly as expensive as a spinlock 
acquire+release fastpath.

Thanks,

	Ingo

WARNING: multiple messages have this Message-ID (diff)
From: Ingo Molnar <mingo@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
	Kevin Hilman <khilman@linaro.org>,
	Russell King <rmk+kernel@arm.linux.org.uk>,
	Thomas Gleixner <tglx@linutronix.de>,
	Steven Rostedt <rostedt@goodmis.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 15:18:10 +0100	[thread overview]
Message-ID: <20130222141810.GB9606@gmail.com> (raw)
In-Reply-To: <1361542150.26780.64.camel@laptop>


* Peter Zijlstra <peterz@infradead.org> wrote:

> On Fri, 2013-02-22 at 13:50 +0100, Frederic Weisbecker wrote:
> > > Argh!! at what cost? 64bit atomics are like expensive. Wouldn't
> > adding
> > > a seqlock be saner?
> > 
> > Not sure. This requires a spinlock in the write side which is called
> > from
> > fast path like the timer interrupt.
> 
> A single spinlock is _way_ cheaper than a ton of cmpxchg8b()s 
> to update a few variables.

Every cmpxchg8b() will be roughly as expensive as a spinlock 
acquire+release fastpath.

Thanks,

	Ingo

  reply	other threads:[~2013-02-22 14:18 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 ` [PATCH 0/2] cpustat: use atomic operations to read/update stats Peter Zijlstra
2013-02-22  8:46   ` 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 [this message]
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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