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Message-ID: <20130222142302.GC18149@somewhere.redhat.com> Date: Fri, 22 Feb 2013 15:23:05 +0100 From: Frederic Weisbecker <fweisbec@...il.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: Peter Zijlstra <peterz@...radead.org>, Kevin Hilman <khilman@...aro.org>, Russell King <rmk+kernel@....linux.org.uk>, Thomas Gleixner <tglx@...utronix.de>, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linaro-kernel@...ts.linaro.org Subject: Re: [PATCH 0/2] cpustat: use atomic operations to read/update stats On Fri, Feb 22, 2013 at 06:21:31AM -0800, Eric Dumazet wrote: > On Fri, 2013-02-22 at 15:09 +0100, Peter Zijlstra 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. > > We also have include/linux/u64_stats_sync.h since 2.6.36 Interesting, we should probably use that instead. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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