Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755462AbbHXTS1 (ORCPT ); Mon, 24 Aug 2015 15:18:27 -0400 Received: from mail-wi0-f171.google.com ([209.85.212.171]:35248 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751959AbbHXTSY (ORCPT ); Mon, 24 Aug 2015 15:18:24 -0400 Message-ID: <1440443901.2891.72.camel@gmail.com> Subject: Re: [PATCH 3/3] sched: Implement interface for cgroup unified hierarchy From: Mike Galbraith To: Tejun Heo Cc: Austin S Hemmelgarn , Paul Turner , Peter Zijlstra , Ingo Molnar , Johannes Weiner , lizefan@huawei.com, cgroups , LKML , kernel-team , Linus Torvalds , Andrew Morton Date: Mon, 24 Aug 2015 21:18:21 +0200 In-Reply-To: <20150824170427.GA27262@mtj.duckdns.org> References: <20150804090711.GL25159@twins.programming.kicks-ass.net> <20150804151017.GD17598@mtj.duckdns.org> <20150805091036.GT25159@twins.programming.kicks-ass.net> <20150805143132.GK17598@mtj.duckdns.org> <20150818203117.GC15739@mtj.duckdns.org> <20150822182916.GE20768@mtj.duckdns.org> <55DB3C76.5010009@gmail.com> <20150824170427.GA27262@mtj.duckdns.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.11 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1804 Lines: 39 On Mon, 2015-08-24 at 13:04 -0400, Tejun Heo wrote: > Hello, Austin. > > On Mon, Aug 24, 2015 at 11:47:02AM -0400, Austin S Hemmelgarn wrote: > > >Just to learn more, what sort of hypervisor support threads are we > > >talking about? They would have to consume considerable amount of cpu > > >cycles for problems like this to be relevant and be dynamic in numbers > > >in a way which letting them competing against vcpus makes sense. Do > > >IO helpers meet these criteria? > > > > > Depending on the configuration, yes they can. VirtualBox has some rather > > CPU intensive threads that aren't vCPU threads (their emulated APIC thread > > immediately comes to mind), and so does QEMU depending on the emulated > > And the number of those threads fluctuate widely and dynamically? > > > hardware configuration (it gets more noticeable when the disk images are > > stored on a SAN and served through iSCSI, NBD, FCoE, or ATAoE, which is > > pretty typical usage for large virtualization deployments). I've seen cases > > first hand where the vCPU's can make no reasonable progress because they are > > constantly getting crowded out by other threads. Hm. Serious CPU starvation would seem to require quite a few hungry threads, but even a few IO threads with kick butt hardware under them could easily tilt fairness heavily in favor of VPUs generating IO. > That alone doesn't require hierarchical resource distribution tho. > Setting nice levels reasonably is likely to alleviate most of the > problem. Unless the CPU controller is in use. -Mike -- 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/