From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Date: Wed, 12 Jan 2005 23:50:05 +0000 Subject: Re: page table lock patch V15 [0/7]: overview Message-Id: <41E5B7AD.40304@yahoo.com.au> List-Id: References: <41E4BCBE.2010001@yahoo.com.au> <20050112014235.7095dcf4.akpm@osdl.org> <20050112104326.69b99298.akpm@osdl.org> <41E5AFE6.6000509@yahoo.com.au> <20050112153033.6e2e4c6e.akpm@osdl.org> In-Reply-To: <20050112153033.6e2e4c6e.akpm@osdl.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Andrew Morton Cc: clameter@sgi.com, 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 Andrew Morton wrote: > Nick Piggin wrote: > >>So my patches cost about 7% in lmbench fork benchmark. > > > OK, well that's the sort of thing we need to understand fully. What sort > of CPU was that on? > That was on a P4, although I've seen pretty similar results on ia64 and other x86 CPUs. Note that this was with my ptl removal patches. I can't see why Christoph's would have _any_ extra overhead as they are, but it looks to me like they're lacking in atomic ops. So I'd expect something similar for Christoph's when they're properly atomic. > Look, -7% on a 2-way versus +700% on a many-way might well be a tradeoff we > agree to take. But we need to fully understand all the costs and benefits. > I think copy_page_range is the one to keep an eye on.