Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932416Ab2FDLlI (ORCPT ); Mon, 4 Jun 2012 07:41:08 -0400 Received: from david.siemens.de ([192.35.17.14]:33806 "EHLO david.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932269Ab2FDLkh (ORCPT ); Mon, 4 Jun 2012 07:40:37 -0400 Message-ID: <4FCC9EAC.9090007@siemens.com> Date: Mon, 04 Jun 2012 13:40:28 +0200 From: Jan Kiszka User-Agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 MIME-Version: 1.0 To: Thomas Gleixner CC: Avi Kivity , Alex Williamson , "kvm@vger.kernel.org" , "mtosatti@redhat.com" , "linux-kernel@vger.kernel.org" , "yongjie.ren@intel.com" Subject: Re: [PATCH] KVM: Use IRQF_ONESHOT for assigned device MSI interrupts References: <20120601161521.26935.25606.stgit@bling.home> <4FC8F042.5050600@siemens.com> <1338570192.23475.25.camel@bling.home> <4FC8F867.7080103@siemens.com> <1338573558.23475.41.camel@bling.home> <4FC90961.8030701@siemens.com> <4FCB2359.9020505@redhat.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3522 Lines: 99 On 2012-06-04 13:21, Thomas Gleixner wrote: > On Sun, 3 Jun 2012, Avi Kivity wrote: > >> On 06/01/2012 09:26 PM, Jan Kiszka wrote: >>> >>>> you suggesting we need a request_edge_threaded_only_irq() API? Thanks, >>> >>> I'm just wondering if that restriction for threaded IRQs is really >>> necessary for all use cases we have. Threaded MSIs do not appear to me >>> like have to be handled that conservatively, but maybe I'm missing some >>> detail. >>> >> >> btw, I'm hoping we can unthread assigned MSIs. If the delivery is >> unicast, we can precalculate everything and all the handler has to do is >> set the IRR, KVM_REQ_EVENT, and kick the vcpu. All of these can be done >> from interrupt context with just RCU locking. > > There is really no need to run MSI/MSI-X interrupts threaded for > KVM. I'm running the patch below for quite some time and it works like > a charm. > > Thanks, > > tglx > ---- > Index: linux-2.6/virt/kvm/assigned-dev.c > =================================================================== > --- linux-2.6.orig/virt/kvm/assigned-dev.c > +++ linux-2.6/virt/kvm/assigned-dev.c > @@ -105,7 +105,7 @@ static irqreturn_t kvm_assigned_dev_thre > } > > #ifdef __KVM_HAVE_MSI > -static irqreturn_t kvm_assigned_dev_thread_msi(int irq, void *dev_id) > +static irqreturn_t kvm_assigned_dev_msi_handler(int irq, void *dev_id) > { > struct kvm_assigned_dev_kernel *assigned_dev = dev_id; > > @@ -117,7 +117,7 @@ static irqreturn_t kvm_assigned_dev_thre > #endif > > #ifdef __KVM_HAVE_MSIX > -static irqreturn_t kvm_assigned_dev_thread_msix(int irq, void *dev_id) > +static irqreturn_t kvm_assigned_dev_msix_handler(int irq, void *dev_id) > { > struct kvm_assigned_dev_kernel *assigned_dev = dev_id; > int index = find_index_from_host_irq(assigned_dev, irq); > @@ -346,9 +346,8 @@ static int assigned_device_enable_host_m > } > > dev->host_irq = dev->dev->irq; > - if (request_threaded_irq(dev->host_irq, NULL, > - kvm_assigned_dev_thread_msi, 0, > - dev->irq_name, dev)) { > + if (request_irq(dev->host_irq, kvm_assigned_dev_msi_handler, 0, > + dev->irq_name, dev)) { > pci_disable_msi(dev->dev); > return -EIO; > } > @@ -373,9 +372,9 @@ static int assigned_device_enable_host_m > return r; > > for (i = 0; i < dev->entries_nr; i++) { > - r = request_threaded_irq(dev->host_msix_entries[i].vector, > - NULL, kvm_assigned_dev_thread_msix, > - 0, dev->irq_name, dev); > + r = request_irq(dev->host_msix_entries[i].vector, > + kvm_assigned_dev_msix_handler, 0, > + dev->irq_name, dev); > if (r) > goto err; > } This may work in practice but has two conceptual problems: - we do not want to run a potential broadcast to all VCPUs to run in a host IRQ handler - crazy user space could have configured the route to end up in the PIC or IOAPIC, and both are not hard-IRQ safe (this should probably be caught on setup) So this shortcut requires some checks before being applied to a specific MSI/MSI-X vector. Taking KVM aside, my general question remains if threaded MSI handlers of all devices really need to apply IRQF_ONESHOT though they should have no use for it. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- 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/