From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH v4] kvm: Use a bitmap for tracking used GSIs Date: Wed, 13 May 2009 17:30:42 +0300 Message-ID: <20090513143042.GG31593@redhat.com> 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; charset=us-ascii Cc: Avi Kivity , kvm@vger.kernel.org, sheng.yang@intel.com To: Alex Williamson Return-path: Received: from mx2.redhat.com ([66.187.237.31]:54239 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752267AbZEMObn (ORCPT ); Wed, 13 May 2009 10:31:43 -0400 Content-Disposition: inline In-Reply-To: <1242224129.9456.6.camel@lappy> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, May 13, 2009 at 08:15:29AM -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. > > Alex Maybe power management powers down the card? Why would that be? Or maybe it detects some error in emulation and resets the card? -- MST