diff options
| author | Ladi Prosek <lprosek@redhat.com> | 2016-08-31 14:00:04 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-11-10 16:36:34 +0100 |
| commit | 50e1c4d90aff5b1f66f9e28a724f3878cb307846 (patch) | |
| tree | 08955e70741073e0ee0abb0f3be300d895afe542 /drivers/virtio | |
| parent | f2d9107bd0a0f86c4b3fb539a2d980ada926c276 (diff) | |
virtio_ring: Make interrupt suppression spec compliant
commit 0ea1e4a6d9b62cf29e210d2b4ba9fd43917522e3 upstream.
According to the spec, if the VIRTIO_RING_F_EVENT_IDX feature bit is
negotiated the driver MUST set flags to 0. Not dirtying the available
ring in virtqueue_disable_cb also has a minor positive performance
impact, improving L1 dcache load missed by ~0.5% in vring_bench.
Writes to the used event field (vring_used_event) are still unconditional.
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/virtio')
| -rw-r--r-- | drivers/virtio/virtio_ring.c | 14 |
1 files changed, 9 insertions, 5 deletions
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index dc2b94142f53..a01a41a41269 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -548,7 +548,8 @@ void virtqueue_disable_cb(struct virtqueue *_vq) if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) { vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT; - vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev, vq->avail_flags_shadow); + if (!vq->event) + vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev, vq->avail_flags_shadow); } } @@ -580,7 +581,8 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq) * entry. Always do both to keep code simple. */ if (vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) { vq->avail_flags_shadow &= ~VRING_AVAIL_F_NO_INTERRUPT; - vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev, vq->avail_flags_shadow); + if (!vq->event) + vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev, vq->avail_flags_shadow); } vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev, last_used_idx = vq->last_used_idx); END_USE(vq); @@ -648,10 +650,11 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) * more to do. */ /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to * either clear the flags bit or point the event index at the next - * entry. Always do both to keep code simple. */ + * entry. Always update the event index to keep code simple. */ if (vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) { vq->avail_flags_shadow &= ~VRING_AVAIL_F_NO_INTERRUPT; - vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev, vq->avail_flags_shadow); + if (!vq->event) + vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev, vq->avail_flags_shadow); } /* TODO: tune this threshold */ bufs = (u16)(vq->avail_idx_shadow - vq->last_used_idx) * 3 / 4; @@ -770,7 +773,8 @@ struct virtqueue *vring_new_virtqueue(unsigned int index, /* No callback? Tell other side not to bother us. */ if (!callback) { vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT; - vq->vring.avail->flags = cpu_to_virtio16(vdev, vq->avail_flags_shadow); + if (!vq->event) + vq->vring.avail->flags = cpu_to_virtio16(vdev, vq->avail_flags_shadow); } /* Put everything in free lists. */ |