Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sat, 3 Aug 2002 20:56:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sat, 3 Aug 2002 20:56:52 -0400 Received: from dsl-213-023-022-101.arcor-ip.net ([213.23.22.101]:18111 "EHLO starship") by vger.kernel.org with ESMTP id ; Sat, 3 Aug 2002 20:56:51 -0400 Content-Type: text/plain; charset=US-ASCII From: Daniel Phillips To: Andrew Morton Subject: Re: [PATCH] Rmap speedup Date: Sun, 4 Aug 2002 03:01:47 +0200 X-Mailer: KMail [version 1.3.2] Cc: linux-kernel@vger.kernel.org References:

<3D4C799C.72D92899@zip.com.au> In-Reply-To: <3D4C799C.72D92899@zip.com.au> MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Message-Id: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1400 Lines: 39 On Sunday 04 August 2002 02:47, Andrew Morton wrote: > Daniel Phillips wrote: > > > > On Saturday 03 August 2002 23:40, Andrew Morton wrote: > > > - total amount of CPU time lost spinning on locks is 1%, mainly > > > in page_add_rmap and zap_pte_range. > > > > > > That's not much spintime. The total system time with this test went > > > from 71 seconds (2.5.26) to 88 seconds (2.5.30). (4.5 seconds per CPU) > > > So all the time is presumably spent waiting on cachelines to come from > > > other CPUs, or from local L2. > > > > Have we tried this one: > > > > static inline unsigned rmap_lockno(pgoff_t index) > > { > > - return (index >> 4) & (ARRAY_SIZE(rmap_locks) - 1); > > + return (index >> 4) & (ARRAY_SIZE(rmap_locks) - 16); > > } > > > > (which puts all the rmap spinlocks in separate cache lines) > > Seems a strange way of doing it? It is a strange way of doing it. I felt like being engigmatic at the time, and no, nothing like that should ever go into production code, it would be better suited to an IOCCC submission. > We'll only ever use four locks this way. Look again: 256 - 16 = 250 = 0xf0. -- Daniel - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/