From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752687AbcEIKjy (ORCPT ); Mon, 9 May 2016 06:39:54 -0400 Received: from vext01.default.vext01.uk0.bigv.io ([213.138.113.174]:27094 "EHLO hudzen10.theunixzoo.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752253AbcEIKjx (ORCPT ); Mon, 9 May 2016 06:39:53 -0400 X-Greylist: delayed 400 seconds by postgrey-1.27 at vger.kernel.org; Mon, 09 May 2016 06:39:53 EDT Date: Mon, 9 May 2016 11:33:12 +0100 From: Edd Barrett To: linux-kernel@vger.kernel.org Subject: Odd interaction between tasket and isolated cores (3.16.x) Message-ID: <20160509103312.GC15143@wilfred.home.dlink.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, I'm experiencing an unexpected behaviour regarding thread scheduling on 3.16.x kernels. What I am trying to do is: run multithreaded benchmarks on a set of isolated cores and have threads balance over the isolated cores. My approach is to boot with an isolcpus kernel argument, then use taskset with an affinity mask so as to force benchmarks onto the isolated set of cores. However, I have found that all threads get bound to one core. Since this is not the case if you don't use taskset, or use a realtime scheduling policy, I tend to think this is a bug, but I am not sure. I've raised a bug here: https://bugzilla.kernel.org/show_bug.cgi?id=116701 Bug description contains a test case and detailed instructions to reproduce. I've also used systemtap to hone in on the troublesome section of code. I think it's to do with affine wake, but I'm not sure. I'd be interested to hear what people think about this. If this is expected behaviour, is there a way to disable affine wakes? Thanks -- Best Regards Edd Barrett http://www.theunixzoo.co.uk