From: Linus Torvalds Subject: Re: [GIT PULL] Ext3 latency fixes Date: Sat, 4 Apr 2009 08:57:28 -0700 (PDT) Message-ID: References: <1238742067-30814-1-git-send-email-tytso@mit.edu> <20090404135719.GA9812@mit.edu> <20090404151649.GE5178@kernel.dk> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: Theodore Tso , Linux Kernel Developers List , Ext4 Developers List To: Jens Axboe Return-path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:56232 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752125AbZDDP76 (ORCPT ); Sat, 4 Apr 2009 11:59:58 -0400 In-Reply-To: <20090404151649.GE5178@kernel.dk> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Sat, 4 Apr 2009, Jens Axboe wrote: > > Big nack on this patch. Ted, this is EXACTLY where I told you we saw big > write regressions (sqlite performance drops by a factor of 4-5). Do a > git log on fs/buffer.c and see the original patch (which does what your > patch does) and the later revert. No idea why you are now suggestion > making that exact change?! Jens, if I can re-create the 'fsync' times (I haven't yet), then the default scheduler _will_ be switched to AS. > Low latency is nice, but not at the cost of 4-5x throughput for real > world cases. I'm sorry, but that fsync thing _is_ a real-world case, and it's the one that a hell of a lot more people care about than some idiotic sqlite throughput issue. You have a test-case now. Consider it a priority, or consider CFQ to be a "for crazy servers that only care about throughput". Quite frankly, the fact that I can see _seconds_ of latencies with a really good SSD is not acceptable. The fact that it is by design is even less so. Latency is more important than throughput. It's that simple. Linus