From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 12 Jan 2005 11:06:00 -0800 (PST) From: Christoph Lameter Subject: Re: page table lock patch V15 [0/7]: overview In-Reply-To: <20050112104326.69b99298.akpm@osdl.org> Message-ID: References: <41E4BCBE.2010001@yahoo.com.au> <20050112014235.7095dcf4.akpm@osdl.org> <20050112104326.69b99298.akpm@osdl.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: nickpiggin@yahoo.com.au, torvalds@osdl.org, ak@muc.de, hugh@veritas.com, linux-mm@kvack.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, benh@kernel.crashing.org List-ID: On Wed, 12 Jan 2005, Andrew Morton wrote: > > So only a very minor improvements for old machines (this one from ~ 98). > > OK. But have you written a test to demonstrate any performance > regressions? From, say, the use of atomic ops on ptes? If I knew of any regressions, I would certain try to deal with them. The test is written to check for concurrent page fault performance and it has repeatedly helped me to find problems with page faults. I have used it for a couple of other patchsets too. If the patch would be available in mm then it certainly would get more exposure and it may become clear that there are some regressions. Introduction of the cmpxchg is one atomic operations that replaces the two spinlock ops typically necessary in an unpatched kernel. Obtaining the spinlock requires an spinlock (which is an atomic operation) and then the release involves a barrier. So there is a net win for all SMP cases as far as I can see. -- 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