Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756324AbaGIPMF (ORCPT ); Wed, 9 Jul 2014 11:12:05 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:18272 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756283AbaGIPMA (ORCPT ); Wed, 9 Jul 2014 11:12:00 -0400 Date: Wed, 9 Jul 2014 11:11:50 -0400 From: Konrad Rzeszutek Wilk To: David Vrabel Cc: Andrew Cooper , konrad@kernel.org, boris.ostrovsky@oracle.com, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org Subject: Re: [Xen-devel] [PATCH v3 1/7] xen-pciback: Document the various parameters and attributes in SysFS Message-ID: <20140709151150.GD28943@laptop.dumpdata.com> References: <1404845909-13563-2-git-send-email-konrad@kernel.org> <53BD32C2.6000306@citrix.com> <20140709135922.GD21837@laptop.dumpdata.com> <53BD4C44.30805@citrix.com> <20140709141354.GG21837@laptop.dumpdata.com> <53BD5026.2030908@citrix.com> <20140709142510.GI21837@laptop.dumpdata.com> <53BD556F.10408@citrix.com> <20140709144744.GC27881@laptop.dumpdata.com> <53BD584B.2030005@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53BD584B.2030005@citrix.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-Source-IP: ucsinet22.oracle.com [156.151.31.94] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 09, 2014 at 03:57:15PM +0100, David Vrabel wrote: > On 09/07/14 15:47, Konrad Rzeszutek Wilk wrote: > > On Wed, Jul 09, 2014 at 03:45:03PM +0100, David Vrabel wrote: > >> On 09/07/14 15:25, Konrad Rzeszutek Wilk wrote: > >>> On Wed, Jul 09, 2014 at 03:22:30PM +0100, Andrew Cooper wrote: > >>>> On 09/07/14 15:13, Konrad Rzeszutek Wilk wrote: > >>>>> On Wed, Jul 09, 2014 at 03:05:56PM +0100, Andrew Cooper wrote: > >>>>>> On 09/07/14 14:59, Konrad Rzeszutek Wilk wrote: > >>>>>>>>> +What: /sys/bus/pci/drivers/pciback/irq_handler_state > >>>>>>>>> +Date: Oct 2011 > >>>>>>>>> +KernelVersion: 3.1 > >>>>>>>>> +Contact: xen-devel@lists.xenproject.org > >>>>>>>>> +Description: > >>>>>>>>> + An option to toggle Xen PCI back to acknowledge (or stop) > >>>>>>>>> + interrupts for the specific device regardless of whether the > >>>>>>>>> + device is shared, enabled, or on a level interrupt line. > >>>>>>>>> + Writing a string of DDDD:BB:DD.F will toggle the state. > >>>>>>>>> + This is Domain:Bus:Device.Function where domain is optional. > >>>>>>>> I do not understand under what circumstances this should be used in. > >>>>>>> So that dom0 does not disable the IRQ line as it would be getting the IRQs > >>>>>>> for the guest as well (because the IRQ line is level and another guest > >>>>>>> uses an PCI device that is using the same line). > >>>>>> Why is this relevant? Xen (and Xen alone) actually controls this aspect > >>>>>> of interrupts. Xen manages passing line level interrupts to any domain > >>>>>> which might have a device hanging off a particular line, and has to wait > >>>>>> until all domains have EOI'd the line until it can clear the interrupt > >>>>>> at the IO-APIC. > >>>>> Because Linux will think there is an IRQ storm as the event->IRQ points > >>>>> to the default one. And then it will mask the event, which means dom0 > >>>>> will mask the PIRQ, and Xen will then also mask the IRQ. > >>>> > >>>> Xen will (and by this I mean 'should', and this was the behaviour last > >>>> time I delved in there) only mask the IRQ if dom0 is the only consumer > >>>> of these interrupts. > >>>> > >>>> For any PCIPassthrough, dom0 will get line interrupts for passed-through > >>>> devices, but in this case pci-back should always handle the line > >>>> interrupts so Linux doesn't block them as an IRQ storm. > >>> > >>> And that is what it does - and this option provides the option to enable/disable > >>> it the system admin wishes to do it. > >> > >> I still don't understand why someone would want to flip the handler to > >> a broken mode. > > > > The intent was to allow you to flip to the 'enable' mode in case Linux > > did not detect it correctly. > > We should not provide sysfs knobs to work around kernel bugs. It is already in the code. This is just a documentation patch. But I can drop this chunk from it if you would like. > > >> The original commit isn't very enlightening either. > > > > Thoughts then on what this documentation patch should say to make it > > clear of its intent? > > I think it should be removed. > > It also has non-standard behaviour of /toggling/ with every write > instead of using a write of a 1 or a 0 like every other sysfs file. The 'unbind' and 'bind' expect an BDF as well and they are part of the SysFS and in documentation. > > David -- 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/