From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id 000076B00C3 for ; Mon, 23 Feb 2009 10:51:58 -0500 (EST) Received: from localhost (smtp.ultrahosting.com [127.0.0.1]) by smtp.ultrahosting.com (Postfix) with ESMTP id 21B3182C333 for ; Mon, 23 Feb 2009 10:56:25 -0500 (EST) Received: from smtp.ultrahosting.com ([74.213.175.254]) by localhost (smtp.ultrahosting.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id wkYQ0qEf01RD for ; Mon, 23 Feb 2009 10:56:25 -0500 (EST) Received: from qirst.com (unknown [74.213.171.31]) by smtp.ultrahosting.com (Postfix) with ESMTP id 8523B82C31A for ; Mon, 23 Feb 2009 10:56:24 -0500 (EST) Date: Mon, 23 Feb 2009 10:43:20 -0500 (EST) From: Christoph Lameter Subject: Re: [PATCH 04/20] Convert gfp_zone() to use a table of precalculated value In-Reply-To: <200902240241.48575.nickpiggin@yahoo.com.au> Message-ID: References: <1235344649-18265-1-git-send-email-mel@csn.ul.ie> <1235344649-18265-5-git-send-email-mel@csn.ul.ie> <200902240241.48575.nickpiggin@yahoo.com.au> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Nick Piggin Cc: Mel Gorman , Linux Memory Management List , Pekka Enberg , Rik van Riel , KOSAKI Motohiro , Johannes Weiner , Nick Piggin , Linux Kernel Mailing List , Lin Ming , Zhang Yanmin List-ID: On Tue, 24 Feb 2009, Nick Piggin wrote: > > Are you sure that this is a benefit? Jumps are forward and pretty short > > and the compiler is optimizing a branch away in the current code. > > Pretty easy to mispredict there, though, especially as you can tend > to get allocations interleaved between kernel and movable (or simply > if the branch predictor is cold there are a lot of branches on x86-64). > > I would be interested to know if there is a measured improvement. It > adds an extra dcache line to the footprint, but OTOH the instructions > you quote is more than one icache line, and presumably Mel's code will > be a lot shorter. Maybe we can come up with a version of gfp_zone that has no branches and no lookup? -- 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