From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 19 Dec 2007 23:04:33 -0800 (PST) From: Christoph Lameter Subject: Re: [patch 02/20] make the inode i_mmap_lock a reader/writer lock In-Reply-To: <200712201040.29040.nickpiggin@yahoo.com.au> Message-ID: References: <20071218211539.250334036@redhat.com> <1198083218.5333.48.camel@localhost> <1198092503.6484.21.camel@twins> <200712201040.29040.nickpiggin@yahoo.com.au> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Peter Zijlstra , Lee Schermerhorn , Rik van Riel , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: > The only reason the x86 ticket locks have the 256 CPu limit is that > if they go any bigger, we can't use the partial registers so would > have to have a few more instructions. x86_64 is going up to 4k or 16k cpus soon for our new hardware. > A 32 bit spinlock would allow 64K cpus (ticket lock has 2 counters, > each would be 16 bits). And it would actually shrink the spinlock in > the case of preempt kernels too (because it would no longer have the > lockbreak field). > > And yes, I'll go out on a limb and say that 64k CPUs ought to be > enough for anyone ;) I think those things need a timeframe applied to it. Thats likely going to be true for the next 3 years (optimistic assessment ;-)). Could you go to 32bit spinlock by default? How about NUMA awareness for the spinlocks? Larger backoff periods for off node lock contentions please. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org