From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Williamson Subject: Re: [PATCH v4] kvm: Use a bitmap for tracking used GSIs Date: Wed, 13 May 2009 08:33:58 -0600 Message-ID: <1242225238.9456.9.camel@lappy> References: <20090512220142.5663.72948.stgit@dl380g6-3.ned.telco.ned.telco> <20090513043835.6696.27384.stgit@dl380g6-3.ned.telco.ned.telco> <4A0A973A.9020502@redhat.com> <1242217702.4786.59.camel@2710p.home> <4A0ABEA8.6030103@redhat.com> <1242219343.4786.66.camel@2710p.home> <4A0AC453.2000907@redhat.com> <1242220276.4786.67.camel@2710p.home> <20090513135502.GA1405@redhat.com> <1242224129.9456.6.camel@lappy> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Avi Kivity , kvm@vger.kernel.org, sheng.yang@intel.com To: "Michael S. Tsirkin" Return-path: Received: from g1t0029.austin.hp.com ([15.216.28.36]:11611 "EHLO g1t0029.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753392AbZEMOd7 (ORCPT ); Wed, 13 May 2009 10:33:59 -0400 In-Reply-To: <1242224129.9456.6.camel@lappy> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, 2009-05-13 at 08:15 -0600, Alex Williamson wrote: > On Wed, 2009-05-13 at 16:55 +0300, Michael S. Tsirkin wrote: > > On Wed, May 13, 2009 at 07:11:16AM -0600, Alex Williamson wrote: > > > On Wed, 2009-05-13 at 16:00 +0300, Avi Kivity wrote: > > > > Alex Williamson wrote: > > > > >> > > > > >> When you say "multiple times", it is several, or a lot more? > > > > >> > > > > >> Maybe it is NAPI? > > > > >> > > > > > > > > > > The system would run out of the ~1000 available GSIs in a minute or two > > > > > with just an e1000e available to the guest. So that's something on the > > > > > order of 10/s. This also causes a printk in the host ever time the > > > > > interrupt in enabled, which can't help performance and gets pretty > > > > > annoying for syslog. I was guessing some kind of interrupt mitigation, > > > > > such as NAPI, but a qlogic FC card seems to do it too (seemingly at a > > > > > slower rate). > > > > > > > > > > > > > I see. And what is the path by which it is disabled? The mask bit in > > > > the MSI entry? > > > > > > Yes, I believe the only path is via a write to the MSI capability in the > > > PCI config space. > > > > > > Alex > > > > Very surprising: I haven't seen any driver disable MSI expect on device > > destructor path. Is this a linux guest? > > Yes, Debian 2.6.26 kernel. I'll check it it behaves the same on newer > upstream kernels and try to figure out why it's doing it. Updating the guest to 2.6.29 seems to fix the interrupt toggling. So it's either something in older kernels or something debian introduced, but that seems unlikely. Alex