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Date: Fri, 22 Aug 2008 11:29:15 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Christoph Lameter <cl@...ux-foundation.org> Cc: 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 Fri, Aug 22, 2008 at 12:14:37PM -0500, Christoph Lameter wrote: > Paul E. McKenney wrote: > > >> RCU is problematic because it lets cachelines get cold. A hot cacheline that > >> is used frequently read and written to by the same cpu is very good thing for > >> performace. > > > > So on your these large boxes, read-only cachelines are preferentially > > ejected from the cache, so that one should write to per-CPU data > > occasionally to keep it resident? Or is the issue the long RCU grace > > periods which allow the structure being freed to age out of all relevant > > caches? (My guess would be the second.) > > The issue are the RCU grace period that are generally long enough to make the > cacheline fall out of all caches. Would it make sense to push the freed-by-RCU memory further up the hierarchy, so that such memory is not mistaken for recently freed hot-in-cache memory? Thanx, Paul -- 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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