Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932188AbbLAXET (ORCPT ); Tue, 1 Dec 2015 18:04:19 -0500 Received: from vserver.eikelenboom.it ([84.200.39.61]:38500 "EHLO smtp.eikelenboom.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932104AbbLAXER (ORCPT ); Tue, 1 Dec 2015 18:04:17 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Date: Wed, 02 Dec 2015 00:00:15 +0100 From: Sander Eikelenboom To: Boris Ostrovsky Cc: Konrad Rzeszutek Wilk , david.vrabel@citrix.com, linux-kernel@vger.kernel.org, xen-devel@lists.xen.org Subject: Re: [Xen-devel] linux 4.4 Regression: 100% cpu usage on idle pv guest under Xen with single vcpu. In-Reply-To: <565E239E.8070507@oracle.com> References: <80dcf47eb772c65a62652d7a56c8ed26@eikelenboom.it> <20151130214513.GF14317@char.us.oracle.com> <16a638d3c5e24963599e621f265181f8@eikelenboom.it> <565CD3A7.1060006@oracle.com> <1454b921884da94b7c1e9f434c13eb4a@eikelenboom.it> <565E239E.8070507@oracle.com> Message-ID: User-Agent: Roundcube Webmail/0.9.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2886 Lines: 87 On 2015-12-01 23:47, Boris Ostrovsky wrote: > On 11/30/2015 05:55 PM, Sander Eikelenboom wrote: >> On 2015-11-30 23:54, Boris Ostrovsky wrote: >>> On 11/30/2015 04:46 PM, Sander Eikelenboom wrote: >>>> On 2015-11-30 22:45, Konrad Rzeszutek Wilk wrote: >>>>> On Sat, Nov 28, 2015 at 04:47:43PM +0100, Sander Eikelenboom wrote: >>>>>> Hi all, >>>>>> >>>>>> I have just tested a 4.4-rc2 kernel (current linus tree) + the tip >>>>>> tree >>>>>> pulled on top. >>>>>> >>>>>> Running this kernel under Xen on PV-guests with multiple vcpus >>>>>> goes well (on >>>>>> idle < 10% cpu usage), >>>>>> but a guest with only a single vcpu doesn't idle at all, it seems >>>>>> a kworker >>>>>> thread is stuck: >>>>>> root 569 98.0 0.0 0 0 ? R 16:02 12:47 >>>>>> [kworker/0:1] >>>>>> >>>>>> Running a 4.3 kernel works fine with a single vpcu, bisecting >>>>>> would probably >>>>>> quite painful since there were some breakages this merge window >>>>>> with respect >>>>>> to Xen pv-guests. >>>>>> >>>>>> There are some differences in the diff's from booting a 4.3, >>>>>> 4.4-single, >>>>>> 4.4-multi cpu boot: >>>>> >>>>> Boris has been tracking a bunch of them. I am attaching the latest >>>>> set of >>>>> patches I've to carry on top of v4.4-rc3. >>>> >>>> Hi Konrad, >>>> >>>> i will test those, see if it fixes all my issues and report back >>> >>> They shouldn't help you ;-( (and I just saw a message from you >>> confirming this) >>> >>> The first one fixes a 32-bit bug (on bare metal too). The second >>> fixes >>> a fatal bug for 32-bit PV guests. The other two are code >>> improvements/cleanup. >> >> One of these patches also fixes a bug i was having with a >> pci-passthrough device in >> a HVM that wasn't working (depending on which dom0-kernel i was using >> (4.3 or 4.4)), >> but didn't report yet. >> >> Fingers crossed but i think this pv-guest single vcpu issue is the >> last i'm troubled by for now ;) > > I could not reproduce this, including with your kernel config file. Hmm that's unpleasant :-\ Hmm other strange thing is it doesn't seem to affect dom0 (which is also a PV guest), but only unprivileged ones All unprivileged pv-guests seem to have the irq issue, but only with a single vcpu i see to get the stuck kworker thread that got my attention, with a 2 vcpu that doesn't seem to happen, but you still get the dmesg output and warnings about hvc) Could it be that: arch/x86/include/asm/i8259.h static inline int nr_legacy_irqs(void) { return legacy_pic->nr_legacy_irqs; } returns something different in some circumstances ? -- Sander > > -boris -- 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/