From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933063AbXB0QDz (ORCPT ); Tue, 27 Feb 2007 11:03:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933070AbXB0QDz (ORCPT ); Tue, 27 Feb 2007 11:03:55 -0500 Received: from x35.xmailserver.org ([64.71.152.41]:2419 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933063AbXB0QDy (ORCPT ); Tue, 27 Feb 2007 11:03:54 -0500 X-AuthUser: davidel@xmailserver.org Date: Tue, 27 Feb 2007 08:03:53 -0800 (PST) From: Davide Libenzi X-X-Sender: davide@alien.or.mcafeemobile.com To: Eric Dumazet cc: Linux Kernel Mailing List , Linus Torvalds , Andrew Morton Subject: Re: [patch] epoll reduced (to 1) number of passes over the ready set ... In-Reply-To: <200702271015.33123.dada1@cosmosbay.com> Message-ID: References: <200702271015.33123.dada1@cosmosbay.com> X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 27 Feb 2007, Eric Dumazet wrote: > On Tuesday 27 February 2007 03:32, Davide Libenzi wrote: > > Epoll is doing multiple passes over the ready set at the moment, because > > of the constraints over the f_op->poll() call. Looking at the code again, > > I noticed that we already hold the epoll semaphore in read, and this > > (together with other locking conditions that hold while doing an > > epoll_wait()) can lead to a smarter way to "ship" events to userspace (in > > a single pass). I added more (even) more comments to the code to explain > > the conditions why certain operations are safe. > > This is a stress application that can be used to test the new code. It > > spwans multiple thread and call epoll_wait() and epoll_ctl() from many > > threads. Stress tested on my dual Opteron 254 w/out any problems. > > Davide, > > This is really cool, because the size of epitem would fit now in 128 bytes > instead of 192 (on x86_64 platforms). So we also reduce memory usage. Yeah, I forgot to mention that I removed the txlink member. > I have one comment : > > > */ > > - list_for_each(lnk, txlist) { > > - epi = list_entry(lnk, struct epitem, txlink); > > + for (eventcnt = 0; !list_empty(txlist) && eventcnt < maxevents;) { > > + epi = list_entry(txlist->next, struct epitem, rdllink); > > Now that we scan the rdllist list once, it may be usefull to use a prefetch() > hint. > > list_for_each() has one prefetch(pos->next) automatically included, but not > your open coded loop. > > I suggest adding after epi = list_entry(txlist->next, struct epitem, rdllink); > prefetch(epi->rdllink.next); Will do in the next version, thx! - Davide