linux-kernel - Re: [PATCH] KVM: Use IRQF_ONESHOT for assigned device MSI interrupts

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Date:	Mon, 4 Jun 2012 13:21:01 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Avi Kivity <avi@...hat.com>
cc:	Jan Kiszka <jan.kiszka@...mens.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"mtosatti@...hat.com" <mtosatti@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"yongjie.ren@...el.com" <yongjie.ren@...el.com>
Subject: Re: [PATCH] KVM: Use IRQF_ONESHOT for assigned device MSI
 interrupts

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;
 	}
--
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