Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751300AbaGIOpI (ORCPT ); Wed, 9 Jul 2014 10:45:08 -0400 Received: from smtp.citrix.com ([66.165.176.89]:25009 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932066AbaGIOpG (ORCPT ); Wed, 9 Jul 2014 10:45:06 -0400 X-IronPort-AV: E=Sophos;i="5.01,631,1400025600"; d="scan'208";a="150983278" Message-ID: <53BD556F.10408@citrix.com> Date: Wed, 9 Jul 2014 15:45:03 +0100 From: David Vrabel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Icedove/24.5.0 MIME-Version: 1.0 To: Konrad Rzeszutek Wilk , Andrew Cooper CC: , , , Subject: Re: [Xen-devel] [PATCH v3 1/7] xen-pciback: Document the various parameters and attributes in SysFS References: <1404845909-13563-1-git-send-email-konrad@kernel.org> <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> In-Reply-To: <20140709142510.GI21837@laptop.dumpdata.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.2.76] X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 original commit isn't very enlightening either. 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/