From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pigeon.gentoo.org ([208.92.234.80] helo=lists.gentoo.org) by finch.gentoo.org with esmtp (Exim 4.60) (envelope-from ) id 1NS88y-0006Yc-0S for garchives@archives.gentoo.org; Tue, 05 Jan 2010 12:04:12 +0000 Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id 990F3E09D1 for ; Tue, 5 Jan 2010 12:04:11 +0000 (UTC) Received: from mail-ew0-f224.google.com (mail-ew0-f224.google.com [209.85.219.224]) by pigeon.gentoo.org (Postfix) with ESMTP id 46A6CE0662 for ; Tue, 5 Jan 2010 11:44:28 +0000 (UTC) Received: by ewy24 with SMTP id 24so19060479ewy.26 for ; Tue, 05 Jan 2010 03:44:27 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:date:message-id:subject :from:to:content-type; bh=RUdwyE0PqrQQybw7bKveXpyo09LqGZihC4AA90UCUAM=; b=tkn0Hxxg54yKiL6ToPgOFtuhKmeI2HChu6VsKlepG8/pMiJo7Sh1fPqLZy6sTnrzgI fqWF6ui98xghPMNS9e2Ho4z02NQQnBzeDHRPgpM9xDRnIDQjThtiL2fWaeg987Cbfd7V vl7yNRY6vkiq+rn+SNJgwvx7BB0jDSdI6Ucow= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:date:message-id:subject:from:to:content-type; b=N+YoEvD3EOuK6mtdvGkXyKrzoe28eG8CH6cFNwjzKMHDq4XClE61mRBVB6z/Mzb2RH TBTJDlzVVxPmTPid/YNeU1oX5XrEXTAuPvAL7FvF7SYV/ntyWRrrCyP4fc7qd07HZXKk CxohFBlXUsCUHA+N4vW7ufnpINviJlS0Hcbhg= Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-server@lists.gentoo.org Reply-to: gentoo-server@lists.gentoo.org MIME-Version: 1.0 Received: by 10.213.24.28 with SMTP id t28mr17328169ebb.92.1262691867614; Tue, 05 Jan 2010 03:44:27 -0800 (PST) Date: Tue, 5 Jan 2010 11:44:27 +0000 Message-ID: <279fbba41001050344q68f80896rf3005d7085ab8940@mail.gmail.com> Subject: [gentoo-server] CFQ low latency mode in 2.6.32 From: Kerin Millar To: gentoo-server@lists.gentoo.org Content-Type: text/plain; charset=ISO-8859-1 X-Archives-Salt: d266b1eb-a22e-464e-b06a-b681f6febb97 X-Archives-Hash: 8f26a2e53b68c6c5d0213293f9b42d74 Hello, While browsing the list of kernel changes in 2.6.32 at kernelnewbies.org, I noticed this: http://kernelnewbies.org/Linux_2_6_32#head-e07f19bb79beab04cb9e68b942c9041b490b71db I'm posting this as a heads up as the article alleges that it can "cause noticeable performance issues". Moreover, it defaults to being swtiched on but is not exposed an option in the kernel build system. It can only be turned off via sysfs: echo 0 > /sys/class/block//queue/iosched/low_latency Therefore, I would advise those who are using CONFIG_IOSCHED_CFQ - and who to intend to upgrade to 2.6.32 - to test the impact of the option upon their respective workloads. Perhaps it's just my interpretation, but I have detected an upstream trend of introducing changes which are either best suited to desktop users or which have had a tendency to introduce performance regressions that are of concern with respect to the server role (gentoo bug #247453 to name but one example). Hopefully this turns out to be a false alarm, but I thought that it would be worth mentioning in any case. Cheers, --Kerin