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Date: Sun, 07 Sep 2008 22:28:01 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Mike Travis <travis@....com>, Ingo Molnar <mingo@...e.hu>, davej@...emonkey.org.uk, David Miller <davem@...emloft.net>, Eric Dumazet <dada1@...mosbay.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, Jack Steiner <steiner@....com>, Jeremy Fitzhardinge <jeremy@...p.org>, Jes Sorensen <jes@....com>, "H. Peter Anvin" <hpa@...or.com>, Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org, Gautham R Shenoy <ego@...ibm.com> Subject: Re: [RFC 07/13] sched: Reduce stack size requirements in kernel/sched.c On Sun, 2008-09-07 at 04:00 -0700, Andrew Morton wrote: > make cpu_hotplug.refcount an atomic_t. That might actually be a worthwhile idea, but it will not make get_online_cpus() atomic. The whole point of get_online_cpus() is to serialize against actual hotplug operations, so it will have to sleep at some point. Now, turning cpu_hotplug.refcount into an atomic_t might be worthwhile because it will reduce the amount of atomic operations in its fastpath from 2 to 1. You'd have to make recount==1 the stable situation and use atomic_inc_unless() and atomic_dec_and_test() in get_online_cpus() and put_online_cpus() resp. that way !refcount can signify a hotplug operation and we'd fall back into the slow paths. -- 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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