From: Yunhong Jiang <yunhong.jiang@linux.intel.com>
To: alex.williamson@redhat.com
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Yunhong Jiang <yunhong.jiang@linux.intel.com>
Subject: [RFC PATCH] VFIO: Add a parameter to force nonthread IRQ
Date: Mon, 26 Oct 2015 18:20:01 -0700 [thread overview]
Message-ID: <1445908801-14732-1-git-send-email-yunhong.jiang@linux.intel.com> (raw)
An option to force VFIO PCI MSI/MSI-X handler as non-threaded IRQ,
even when CONFIG_IRQ_FORCED_THREADING=y. This is uselful when
assigning a device to a guest with low latency requirement since it
reduce the context switch to/from the IRQ thread.
An experiment was conducted on a HSW platform for 1 minutes, with the
guest vCPU bound to isolated pCPU. The assigned device triggered the
interrupt every 1ms. The average EXTERNAL_INTERRUPT exit handling time
is dropped from 5.3us to 2.2us.
Another choice is to change VFIO_DEVICE_SET_IRQS ioctl, to apply this
option only to specific devices when in kernel irq_chip is enabled. It
provides more flexibility but is more complex, not sure if we need go
through that way.
Signed-off-by: Yunhong Jiang <yunhong.jiang@linux.intel.com>
---
drivers/vfio/pci/vfio_pci_intrs.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
index 1f577b4..ca1f95a 100644
--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/drivers/vfio/pci/vfio_pci_intrs.c
@@ -22,9 +22,13 @@
#include <linux/vfio.h>
#include <linux/wait.h>
#include <linux/slab.h>
+#include <linux/module.h>
#include "vfio_pci_private.h"
+static bool nonthread_msi = 1;
+module_param(nonthread_msi, bool, 0444);
+
/*
* INTx
*/
@@ -313,6 +317,7 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_device *vdev,
char *name = msix ? "vfio-msix" : "vfio-msi";
struct eventfd_ctx *trigger;
int ret;
+ unsigned long irqflags = 0;
if (vector >= vdev->num_ctx)
return -EINVAL;
@@ -352,7 +357,10 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_device *vdev,
pci_write_msi_msg(irq, &msg);
}
- ret = request_irq(irq, vfio_msihandler, 0,
+ if (nonthread_msi)
+ irqflags = IRQF_NO_THREAD;
+
+ ret = request_irq(irq, vfio_msihandler, irqflags,
vdev->ctx[vector].name, trigger);
if (ret) {
kfree(vdev->ctx[vector].name);
--
1.8.3.1
next reply other threads:[~2015-10-27 1:31 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-27 1:20 Yunhong Jiang [this message]
2015-10-27 3:37 ` [RFC PATCH] VFIO: Add a parameter to force nonthread IRQ Alex Williamson
2015-10-27 6:35 ` Yunhong Jiang
2015-10-27 9:29 ` Paolo Bonzini
2015-10-27 21:26 ` Yunhong Jiang
2015-10-28 0:44 ` Paolo Bonzini
2015-10-28 16:00 ` Alex Williamson
2015-10-28 17:05 ` Paolo Bonzini
2015-10-28 23:54 ` Marcelo Tosatti
2015-10-29 3:11 ` Alex Williamson
2015-10-29 9:45 ` Paolo Bonzini
2015-10-30 6:16 ` Yunhong Jiang
2015-11-02 9:17 ` Paolo Bonzini
2015-10-28 17:50 ` Yunhong Jiang
2015-10-28 18:18 ` Alex Williamson
2015-10-28 21:46 ` Yunhong Jiang
2015-10-28 18:28 ` Paolo Bonzini
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