Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932407AbXAGFkX (ORCPT ); Sun, 7 Jan 2007 00:40:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932405AbXAGFkX (ORCPT ); Sun, 7 Jan 2007 00:40:23 -0500 Received: from smtp.osdl.org ([65.172.181.24]:33110 "EHLO smtp.osdl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932403AbXAGFkW (ORCPT ); Sun, 7 Jan 2007 00:40:22 -0500 Date: Sat, 6 Jan 2007 21:39:42 -0800 (PST) From: Linus Torvalds To: "H. Peter Anvin" cc: git@vger.kernel.org, nigel@nigel.suspend2.net, "J.H." , Randy Dunlap , Andrew Morton , Pavel Machek , kernel list , webmaster@kernel.org Subject: Re: How git affects kernel.org performance In-Reply-To: <45A083F2.5000000@zytor.com> Message-ID: References: <20061214223718.GA3816@elf.ucw.cz> <20061216094421.416a271e.randy.dunlap@oracle.com> <20061216095702.3e6f1d1f.akpm@osdl.org> <458434B0.4090506@oracle.com> <1166297434.26330.34.camel@localhost.localdomain> <1166304080.13548.8.camel@nigel.suspend2.net> <459152B1.9040106@zytor.com> <1168140954.2153.1.camel@nigel.suspend2.net> <45A08269.4050504@zytor.com> <45A083F2.5000000@zytor.com> 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 Content-Length: 1615 Lines: 36 On Sat, 6 Jan 2007, H. Peter Anvin wrote: > > During extremely high load, it appears that what slows kernel.org down more > than anything else is the time that each individual getdents() call takes. > When I've looked this I've observed times from 200 ms to almost 2 seconds! > Since an unpacked *OR* unpruned git tree adds 256 directories to a cleanly > packed tree, you can do the math yourself. "getdents()" is totally serialized by the inode semaphore. It's one of the most expensive system calls in Linux, partly because of that, and partly because it has to call all the way down into the filesystem in a way that almost no other common system call has to (99% of all filesystem calls can be handled basically at the VFS layer with generic caches - but not getdents()). So if there are concurrent readdirs on the same directory, they get serialized. If there is any file creation/deletion activity in the directory, it serializes getdents(). To make matters worse, I don't think it has any read-ahead at all when you use hashed directory entries. So if you have cold-cache case, you'll read every single block totally individually, and serialized. One block at a time (I think the non-hashed case is likely also suspect, but that's a separate issue) In other words, I'm not at all surprised it hits on filldir time. Especially on ext3. Linus - 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/