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From: Alex Williamson <alex.williamson@hp.com>
To: qemu-devel@nongnu.org
Cc: kvm@vger.kernel.org, alex.williamson@hp.com
Subject: [PATCH] qemu:virtio: Allow guest to defer VIRTIO_F_NOTIFY_ON_EMPTY
Date: Thu, 19 Mar 2009 10:21:59 -0600	[thread overview]
Message-ID: <20090319162118.24068.98794.stgit@kvm.aw> (raw)

There may be cases where the guest does not want the avail queue
interrupt, even when it's empty.  For the virtio-net case, the
guest may use a different buffering scheme or decide polling for
used buffers is more efficient.  This can be accomplished by simply
checking for whether the guest has acknowledged the existing notify
on empty flag.

Signed-off-by: Alex Williamson <alex.williamson@hp.com>
---

 hw/virtio.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/hw/virtio.c b/hw/virtio.c
index b94ab0f..08ea16d 100644
--- a/hw/virtio.c
+++ b/hw/virtio.c
@@ -726,9 +726,10 @@ VirtQueue *virtio_add_queue(VirtIODevice *vdev, int queue_size,
 
 void virtio_notify(VirtIODevice *vdev, VirtQueue *vq)
 {
-    /* Always notify when queue is empty */
-    if ((vq->inuse || vring_avail_idx(vq) != vq->last_avail_idx) &&
-        (vring_avail_flags(vq) & VRING_AVAIL_F_NO_INTERRUPT))
+    /* Always notify when queue is empty (when feature acknowledge) */
+    if ((vring_avail_flags(vq) & VRING_AVAIL_F_NO_INTERRUPT) &&
+        (!(vdev->features & (1 << VIRTIO_F_NOTIFY_ON_EMPTY)) ||
+         (vq->inuse || vring_avail_idx(vq) != vq->last_avail_idx)))
         return;
 
     vdev->isr |= 0x01;


WARNING: multiple messages have this Message-ID (diff)
From: Alex Williamson <alex.williamson@hp.com>
To: qemu-devel@nongnu.org
Cc: alex.williamson@hp.com, kvm@vger.kernel.org
Subject: [Qemu-devel] [PATCH] qemu:virtio: Allow guest to defer VIRTIO_F_NOTIFY_ON_EMPTY
Date: Thu, 19 Mar 2009 10:21:59 -0600	[thread overview]
Message-ID: <20090319162118.24068.98794.stgit@kvm.aw> (raw)

There may be cases where the guest does not want the avail queue
interrupt, even when it's empty.  For the virtio-net case, the
guest may use a different buffering scheme or decide polling for
used buffers is more efficient.  This can be accomplished by simply
checking for whether the guest has acknowledged the existing notify
on empty flag.

Signed-off-by: Alex Williamson <alex.williamson@hp.com>
---

 hw/virtio.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/hw/virtio.c b/hw/virtio.c
index b94ab0f..08ea16d 100644
--- a/hw/virtio.c
+++ b/hw/virtio.c
@@ -726,9 +726,10 @@ VirtQueue *virtio_add_queue(VirtIODevice *vdev, int queue_size,
 
 void virtio_notify(VirtIODevice *vdev, VirtQueue *vq)
 {
-    /* Always notify when queue is empty */
-    if ((vq->inuse || vring_avail_idx(vq) != vq->last_avail_idx) &&
-        (vring_avail_flags(vq) & VRING_AVAIL_F_NO_INTERRUPT))
+    /* Always notify when queue is empty (when feature acknowledge) */
+    if ((vring_avail_flags(vq) & VRING_AVAIL_F_NO_INTERRUPT) &&
+        (!(vdev->features & (1 << VIRTIO_F_NOTIFY_ON_EMPTY)) ||
+         (vq->inuse || vring_avail_idx(vq) != vq->last_avail_idx)))
         return;
 
     vdev->isr |= 0x01;

             reply	other threads:[~2009-03-19 16:25 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-03-19 16:21 Alex Williamson [this message]
2009-03-19 16:21 ` [Qemu-devel] [PATCH] qemu:virtio: Allow guest to defer VIRTIO_F_NOTIFY_ON_EMPTY Alex Williamson
2009-03-20 17:31 ` Anthony Liguori
2009-03-20 17:31   ` [Qemu-devel] " Anthony Liguori

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