From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758747AbYGAPnu (ORCPT ); Tue, 1 Jul 2008 11:43:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754925AbYGAPnl (ORCPT ); Tue, 1 Jul 2008 11:43:41 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:57762 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751820AbYGAPnk (ORCPT ); Tue, 1 Jul 2008 11:43:40 -0400 Date: Tue, 1 Jul 2008 08:43:26 -0700 (PDT) From: Linus Torvalds To: Paul Mundt cc: Hideo Saito , linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: follow_page() performance regressions In-Reply-To: <20080701052543.GA4726@linux-sh.org> Message-ID: References: <20080701.132439.68562265.saito@densan.co.jp> <20080701052543.GA4726@linux-sh.org> User-Agent: Alpine 1.10 (LFD 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 1 Jul 2008, Paul Mundt wrote: > > So yes, the ZERO_PAGE handling in follow_page() is causing the slow-down here. I suspect it could be any of: - actual code generation differences in follow_page() (some SH person needs to check that) - some cache issue on SH. ZERO_PAGE is a single page at a fixed virtual address, while it used to populate the page tables with individual pages. Normally, this should be *better* for caching, but maybe there is some conflict? What kind of caches does SH have (virtually indexed?) - hackbench relying on follow_page() to populate the page tables, which it no longer does for anonymous areas (using ZERO_PAGE directly instead). Again, normally this would speed things up (fewer TLB misses etc), but if it then causes a new page fault that used to have been covered by follow_page(), who knows? What does hackbench actually do? Anybody? Linus