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[Qemu-devel] [PATCH 08/10] virtio: cache used_idx in a VirtQueue field
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH 08/10] virtio: cache used_idx in a VirtQueue field |
Date: |
Sun, 31 Jan 2016 11:29:04 +0100 |
From: Vincenzo Maffione <address@hidden>
Accessing used_idx in the VQ requires an expensive access to
guest physical memory. Before this patch, 3 accesses are normally
done for each pop/push/notify call. However, since the used_idx is
only written by us, we can track it in our internal data structure.
Signed-off-by: Vincenzo Maffione <address@hidden>
Message-Id: <address@hidden>
Reviewed-by: Cornelia Huck <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
---
hw/virtio/virtio.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 2433866..5116a2e 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -71,6 +71,9 @@ struct VirtQueue
{
VRing vring;
uint16_t last_avail_idx;
+
+ uint16_t used_idx;
+
/* Last used index value we have signalled on */
uint16_t signalled_used;
@@ -170,6 +173,7 @@ static inline void vring_used_idx_set(VirtQueue *vq,
uint16_t val)
hwaddr pa;
pa = vq->vring.used + offsetof(VRingUsed, idx);
virtio_stw_phys(vq->vdev, pa, val);
+ vq->used_idx = val;
}
static inline void vring_used_flags_set_bit(VirtQueue *vq, int mask)
@@ -261,7 +265,7 @@ void virtqueue_fill(VirtQueue *vq, const VirtQueueElement
*elem,
virtqueue_unmap_sg(vq, elem, len);
- idx = (idx + vring_used_idx(vq)) % vq->vring.num;
+ idx = (idx + vq->used_idx) % vq->vring.num;
/* Get a pointer to the next entry in the used ring. */
vring_used_ring_id(vq, idx, elem->index);
@@ -274,7 +278,7 @@ void virtqueue_flush(VirtQueue *vq, unsigned int count)
/* Make sure buffer is written before we update index. */
smp_wmb();
trace_virtqueue_flush(vq, count);
- old = vring_used_idx(vq);
+ old = vq->used_idx;
new = old + count;
vring_used_idx_set(vq, new);
vq->inuse -= count;
@@ -782,6 +786,7 @@ void virtio_reset(void *opaque)
vdev->vq[i].vring.avail = 0;
vdev->vq[i].vring.used = 0;
vdev->vq[i].last_avail_idx = 0;
+ vdev->vq[i].used_idx = 0;
virtio_queue_set_vector(vdev, i, VIRTIO_NO_VECTOR);
vdev->vq[i].signalled_used = 0;
vdev->vq[i].signalled_used_valid = false;
@@ -1161,7 +1166,7 @@ static bool vring_notify(VirtIODevice *vdev, VirtQueue
*vq)
v = vq->signalled_used_valid;
vq->signalled_used_valid = true;
old = vq->signalled_used;
- new = vq->signalled_used = vring_used_idx(vq);
+ new = vq->signalled_used = vq->used_idx;
return !v || vring_need_event(vring_get_used_event(vq), new, old);
}
@@ -1573,6 +1578,7 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int
version_id)
vdev->vq[i].last_avail_idx, nheads);
return -1;
}
+ vdev->vq[i].used_idx = vring_used_idx(&vdev->vq[i]);
}
}
--
2.5.0
- [Qemu-devel] [PATCH v2 00/10] virtio/vring: optimization patches, Paolo Bonzini, 2016/01/31
- [Qemu-devel] [PATCH 01/10] virtio: move VirtQueueElement at the beginning of the structs, Paolo Bonzini, 2016/01/31
- [Qemu-devel] [PATCH 03/10] virtio: introduce qemu_get/put_virtqueue_element, Paolo Bonzini, 2016/01/31
- [Qemu-devel] [PATCH 04/10] virtio: introduce virtqueue_alloc_element, Paolo Bonzini, 2016/01/31
- [Qemu-devel] [PATCH 05/10] virtio: slim down allocation of VirtQueueElements, Paolo Bonzini, 2016/01/31
- [Qemu-devel] [PATCH 06/10] vring: slim down allocation of VirtQueueElements, Paolo Bonzini, 2016/01/31
- [Qemu-devel] [PATCH 07/10] virtio: combine the read of a descriptor, Paolo Bonzini, 2016/01/31
- [Qemu-devel] [PATCH 08/10] virtio: cache used_idx in a VirtQueue field,
Paolo Bonzini <=
- [Qemu-devel] [PATCH 02/10] virtio: move allocation to virtqueue_pop/vring_pop, Paolo Bonzini, 2016/01/31
- [Qemu-devel] [PATCH 09/10] virtio: read avail_idx from VQ only when necessary, Paolo Bonzini, 2016/01/31
- [Qemu-devel] [PATCH 10/10] virtio: combine write of an entry into used ring, Paolo Bonzini, 2016/01/31