linux-kernel - Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall

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Date:	Fri, 24 Nov 2006 15:47:56 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oleg Nesterov <oleg@...sign.ru>
cc:	"Paul E. McKenney" <paulmck@...ibm.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync

On Fri, 24 Nov 2006, Oleg Nesterov wrote:

> Ok, synchronize_xxx() passed 1 hour rcutorture test on dual P-III.
> 
> It behaves the same as srcu but optimized for writers. The fast path
> for synchronize_xxx() is mutex_lock() + atomic_read() + mutex_unlock().
> The slow path is __wait_event(), no polling. However, the reader does
> atomic inc/dec on lock/unlock, and the counters are not per-cpu.
> 
> Jens, is it ok for you? Alan, Paul, what is your opinion?

Given that you aren't using per-cpu data, why not just rely on a spinlock?  
Then everything will be simple and easy to verify, with no need to worry 
about atomic instructions or memory barriers.

Alan

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