From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754984Ab2EJK3u (ORCPT ); Thu, 10 May 2012 06:29:50 -0400 Received: from mailout-de.gmx.net ([213.165.64.22]:32954 "HELO mailout-de.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750848Ab2EJK3t (ORCPT ); Thu, 10 May 2012 06:29:49 -0400 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX1+a+rFawSSagvfJolhBZR4H8ysRdo9zwqefUfhAER kCe5ApPfHKSINp Message-ID: <1336645785.25483.3.camel@marge.simpson.net> Subject: Re: Scheduler still seems awful with x264, worse with patches From: Mike Galbraith To: Jason Garrett-Glaser Cc: Linux Kernel Mailing List Date: Thu, 10 May 2012 12:29:45 +0200 In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2012-05-09 at 09:00 -0700, Jason Garrett-Glaser wrote: > Many months ago, the topic of CFS's inefficiencies with x264 came up > and some improvements were made, but BFS and Windows still stayed a > little bit in the lead. This seemed to be because of a mix of two > issues. Firstly, a combination of relatively short-lived jobs (x264 > uses a thread pool, so the actual threads are long-lived). Secondly, > in frame threads, heavy dependencies between threads, benefiting > greatly from a dumb scheduler. Thirdly, in sliced threads -- the > focus of this post -- the best scheduling approach is to simply spread > them throughout the cores and do nothing, so again, a dumb scheduler > will do the right thing. > > Recently I tried multithreading x264's lookahead for a customer. The > lookahead previously wasn't threaded, causing bottlenecks with many > cores and threads. I do my development mainly on Windows, and the > patch looked to be quite a success, with nice performance boosts for > many target use-cases. > > And then I ran it on Linux and it choked horribly. > > The patch is here: > https://github.com/DarkShikari/x264-devel/commit/99e830f1581eac3cf30f07b1d6c6c32bae1725c8 > . To replicate the test, simply test that version against the > previous version. My guess is the reason it chokes is that it > involves spawning even *shorter*-lived jobs than x264 typically does, > something that CFS seems to simply collapse on. > > Here's some stats from a recent kernel: > > SD encoding (before -> after patch): > CFS: 325.49 +/- 1.22 fps -> 251.68 +/- 2.32 fps > BFS: 334.94 +/- 0.59 fps -> 344.47 +/- 0.68 fps > > HD encoding (before -> after patch): > CFS: 39.05 +/- 0.22 fps -> 40.56 +/- 0.23 fps > BFS: 40.15 +/- 0.05 fps -> 44.89 +/- 0.05 fps > > As can be seen, the longer the threads live (the lower the fps), the > less horrific the penalty is. Furthermore, though I don't have > numbers, using schedtool -R -p 1 does basically as well as BFS in > eliminating the problem. Naturally, this is not really a solution as > it requires root. > > To replicate this test, a commandline like this should work on any > cached raw input file (a collection of free raw videos can be found > here if you don't like making your own: > http://media.xiph.org/video/derf/ ): > > ./x264 --preset superfast --tune zerolatency --threads X input -o /dev/null On my Q6600 box, neither scheduler (identical configs) seems to like --tune zerolatency much. # ultrafast x264 --quiet --no-progress --preset ultrafast --no-scenecut --sync-lookahead 0 --qp 20 -o /dev/null --threads $1 ./soccer_4cif.y4m x264 --quiet --no-progress --preset ultrafast --tune zerolatency --no-scenecut --sync-lookahead 0 --qp 20 -o /dev/null --threads $1 ./soccer_4cif.y4m x264 --quiet --no-progress --preset ultrafast --tune zerolatency -o /dev/null --threads $1 ./soccer_4cif.y4m 3.3.0-bfs 3.3.0-cfs marge:~/tmp # ./x264.sh 8 encoded 600 frames, 449.63 fps 400.20 fps encoded 600 frames, 355.00 fps 304.12 fps encoded 600 frames, 305.65 fps 267.25 fps marge:~/tmp # schedctl -I ./x264.sh 8 encoded 600 frames, 475.00 fps 483.19 fps encoded 600 frames, 364.72 fps 278.37 fps encoded 600 frames, 311.69 fps 256.25 fps marge:~/tmp # schedctl -R ./x264.sh 8 encoded 600 frames, 454.70 fps 489.00 fps encoded 600 frames, 358.83 fps 365.61 fps encoded 600 frames, 308.81 fps 310.46 fps