From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: page table lock patch V15 [0/7]: overview II From: Nick Piggin In-Reply-To: References: <41E5AFE6.6000509@yahoo.com.au> <20050112153033.6e2e4c6e.akpm@osdl.org> <41E5B7AD.40304@yahoo.com.au> <41E5BC60.3090309@yahoo.com.au> <20050113031807.GA97340@muc.de> <20050113180205.GA17600@muc.de> <20050114043944.GB41559@muc.de> Content-Type: text/plain Date: Fri, 14 Jan 2005 15:59:02 +1100 Message-Id: <1105678742.5402.109.camel@npiggin-nld.site> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andi Kleen Cc: clameter@sgi.com, Andrew Morton , torvalds@osdl.org, hugh@veritas.com, linux-mm@kvack.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, benh@kernel.crashing.org List-ID: On Fri, 2005-01-14 at 05:52 +0100, Andi Kleen wrote: > Andi Kleen writes: > > As you can see cmpxchg is slightly faster for the cache hot case, > > but incredibly slow for cache cold (probably because it does something > > nasty on the bus). This is pretty consistent to Intel and AMD CPUs. > > Given that page tables are likely more often cache cold than hot > > I would use the lazy variant. > > Sorry, my benchmark program actually had a bug (first loop included > page faults). Here are updated numbers. They are somewhat different: > > Athlon 64: > readpte hot 25 > readpte cold 171 > readpte_cmp hot 18 > readpte_cmp cold 162 > > Nocona: > readpte hot 118 > readpte cold 443 > readpte_cmp hot 22 > readpte_cmp cold 224 > > The difference is much smaller here. Assuming cache cold cmpxchg8b is > better, at least on the Intel CPUs which have a slow rmb(). > I have a question for the x86 gurus. We're currently using the lock prefix for set_64bit. This will lock the bus for the RMW cycle, but is it a prerequisite for the atomic 64-bit store? Even on UP? Find local movie times and trailers on Yahoo! Movies. http://au.movies.yahoo.com -- 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: aart@kvack.org