Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755055AbaGIO5k (ORCPT ); Wed, 9 Jul 2014 10:57:40 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:33481 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751268AbaGIO5j (ORCPT ); Wed, 9 Jul 2014 10:57:39 -0400 X-IronPort-AV: E=Sophos;i="5.01,631,1400025600"; d="scan'208";a="151263804" Message-ID: <53BD584B.2030005@citrix.com> Date: Wed, 9 Jul 2014 15:57:15 +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 CC: Andrew Cooper , , , , 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> <53BD556F.10408@citrix.com> <20140709144744.GC27881@laptop.dumpdata.com> In-Reply-To: <20140709144744.GC27881@laptop.dumpdata.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.2.76] X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. >> 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. 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/