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Date: Mon, 25 Aug 2008 17:51:32 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Christoph Lameter <cl@...ux-foundation.org> Cc: paulmck@...ux.vnet.ibm.com, Pekka Enberg <penberg@...helsinki.fi>, Ingo Molnar <mingo@...e.hu>, Jeremy Fitzhardinge <jeremy@...p.org>, Nick Piggin <nickpiggin@...oo.com.au>, Andi Kleen <andi@...stfloor.org>, "Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>, Suresh Siddha <suresh.b.siddha@...el.com>, Jens Axboe <jens.axboe@...cle.com>, Rusty Russell <rusty@...tcorp.com.au>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 2/2] smp_call_function: use rwlocks on queues rather than rcu On Mon, 2008-08-25 at 10:46 -0500, Christoph Lameter wrote: > Peter Zijlstra wrote: > > > > If we combine these two cases, and flip the counter as soon as we've > > enqueued one callback, unless we're already waiting for a grace period > > to end - which gives us a longer window to collect callbacks. > > > > And then the rcu_read_unlock() can do: > > > > if (dec_and_zero(my_counter) && my_index == dying) > > raise_softirq(RCU) > > > > to fire off the callback stuff. > > > > /me ponders - there must be something wrong with that... > > > > Aaah, yes, the dec_and_zero is non trivial due to the fact that its a > > distributed counter. Bugger.. > > Then lets make it per cpu. If we get the cpu ops in then dec_and_zero would be > very cheap. Hmm, perhaps that might work for classic RCU, as that disables preemption and thus the counters should always be balanced. -- 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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