| Message ID | 20210526082423.47837-4-mst@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v3,1/4] virtio_net: move tx vq operation under tx queue lock | expand |
在 2021/5/26 下午4:24, Michael S. Tsirkin 写道: > virtio_disable_cb is currently a nop for split ring with event index. > This is because it used to be always called from a callback when we know > device won't trigger more events until we update the index. However, > now that we run with interrupts enabled a lot we also poll without a > callback so that is different: disabling callbacks will help reduce the > number of spurious interrupts. > Further, if using event index with a packed ring, and if being called > from a callback, we actually do disable interrupts which is unnecessary. > > Fix both issues by tracking whenever we get a callback. If that is > the case disabling interrupts with event index can be a nop. This seems unnecessary: 1) we check avail_flags_shadow before touching touching the index 2) The nop is not good at least for split, if we choose a suitable event index, it can help to reduce the chance of 1/N interrupt, (see below). > If not the case disable interrupts. Note: with a split ring > there's no explicit "no interrupts" value. For now we write > a fixed value so our chance of triggering an interupt > is 1/ring size. 1/65535 actually? If yes, do we still need this trick? > It's probably better to write something > related to the last used index there to reduce the chance > even further. For now I'm keeping it simple. > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > --- > drivers/virtio/virtio_ring.c | 26 +++++++++++++++++++++++++- > 1 file changed, 25 insertions(+), 1 deletion(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 71e16b53e9c1..88f0b16b11b8 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -113,6 +113,9 @@ struct vring_virtqueue { > /* Last used index we've seen. */ > u16 last_used_idx; > > + /* Hint for event idx: already triggered no need to disable. */ > + bool event_triggered; > + > union { > /* Available for split ring */ > struct { > @@ -739,7 +742,10 @@ static void virtqueue_disable_cb_split(struct virtqueue *_vq) > > if (!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) { > vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT; > - if (!vq->event) > + if (vq->event) > + /* TODO: this is a hack. Figure out a cleaner value to write. */ > + vring_used_event(&vq->split.vring) = 0x0; used_idx or last_used_idx seems better here. > + else > vq->split.vring.avail->flags = > cpu_to_virtio16(_vq->vdev, > vq->split.avail_flags_shadow); > @@ -1605,6 +1611,7 @@ static struct virtqueue *vring_create_virtqueue_packed( > vq->weak_barriers = weak_barriers; > vq->broken = false; > vq->last_used_idx = 0; > + vq->event_triggered = false; > vq->num_added = 0; > vq->packed_ring = true; > vq->use_dma_api = vring_use_dma_api(vdev); > @@ -1919,6 +1926,12 @@ void virtqueue_disable_cb(struct virtqueue *_vq) > { > struct vring_virtqueue *vq = to_vvq(_vq); > > + /* If device triggered an event already it won't trigger one again: > + * no need to disable. > + */ > + if (vq->event_triggered) > + return; > + > if (vq->packed_ring) > virtqueue_disable_cb_packed(_vq); > else > @@ -1942,6 +1955,9 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq) > { > struct vring_virtqueue *vq = to_vvq(_vq); > > + if (vq->event_triggered) > + vq->event_triggered = false; > + > return vq->packed_ring ? virtqueue_enable_cb_prepare_packed(_vq) : > virtqueue_enable_cb_prepare_split(_vq); > } > @@ -2005,6 +2021,9 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) > { > struct vring_virtqueue *vq = to_vvq(_vq); > > + if (vq->event_triggered) > + vq->event_triggered = false; > + > return vq->packed_ring ? virtqueue_enable_cb_delayed_packed(_vq) : > virtqueue_enable_cb_delayed_split(_vq); > } Miss the case of virtqueue_enable_cb()? Thanks > @@ -2044,6 +2063,10 @@ irqreturn_t vring_interrupt(int irq, void *_vq) > if (unlikely(vq->broken)) > return IRQ_HANDLED; > > + /* Just a hint for performance: so it's ok that this can be racy! */ > + if (vq->event) > + vq->event_triggered = true; > + > pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback); > if (vq->vq.callback) > vq->vq.callback(&vq->vq); > @@ -2083,6 +2106,7 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index, > vq->weak_barriers = weak_barriers; > vq->broken = false; > vq->last_used_idx = 0; > + vq->event_triggered = false; > vq->num_added = 0; > vq->use_dma_api = vring_use_dma_api(vdev); > #ifdef DEBUG
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 71e16b53e9c1..88f0b16b11b8 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -113,6 +113,9 @@ struct vring_virtqueue { /* Last used index we've seen. */ u16 last_used_idx; + /* Hint for event idx: already triggered no need to disable. */ + bool event_triggered; + union { /* Available for split ring */ struct { @@ -739,7 +742,10 @@ static void virtqueue_disable_cb_split(struct virtqueue *_vq) if (!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) { vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT; - if (!vq->event) + if (vq->event) + /* TODO: this is a hack. Figure out a cleaner value to write. */ + vring_used_event(&vq->split.vring) = 0x0; + else vq->split.vring.avail->flags = cpu_to_virtio16(_vq->vdev, vq->split.avail_flags_shadow); @@ -1605,6 +1611,7 @@ static struct virtqueue *vring_create_virtqueue_packed( vq->weak_barriers = weak_barriers; vq->broken = false; vq->last_used_idx = 0; + vq->event_triggered = false; vq->num_added = 0; vq->packed_ring = true; vq->use_dma_api = vring_use_dma_api(vdev); @@ -1919,6 +1926,12 @@ void virtqueue_disable_cb(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); + /* If device triggered an event already it won't trigger one again: + * no need to disable. + */ + if (vq->event_triggered) + return; + if (vq->packed_ring) virtqueue_disable_cb_packed(_vq); else @@ -1942,6 +1955,9 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); + if (vq->event_triggered) + vq->event_triggered = false; + return vq->packed_ring ? virtqueue_enable_cb_prepare_packed(_vq) : virtqueue_enable_cb_prepare_split(_vq); } @@ -2005,6 +2021,9 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); + if (vq->event_triggered) + vq->event_triggered = false; + return vq->packed_ring ? virtqueue_enable_cb_delayed_packed(_vq) : virtqueue_enable_cb_delayed_split(_vq); } @@ -2044,6 +2063,10 @@ irqreturn_t vring_interrupt(int irq, void *_vq) if (unlikely(vq->broken)) return IRQ_HANDLED; + /* Just a hint for performance: so it's ok that this can be racy! */ + if (vq->event) + vq->event_triggered = true; + pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback); if (vq->vq.callback) vq->vq.callback(&vq->vq); @@ -2083,6 +2106,7 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index, vq->weak_barriers = weak_barriers; vq->broken = false; vq->last_used_idx = 0; + vq->event_triggered = false; vq->num_added = 0; vq->use_dma_api = vring_use_dma_api(vdev); #ifdef DEBUG
virtio_disable_cb is currently a nop for split ring with event index. This is because it used to be always called from a callback when we know device won't trigger more events until we update the index. However, now that we run with interrupts enabled a lot we also poll without a callback so that is different: disabling callbacks will help reduce the number of spurious interrupts. Further, if using event index with a packed ring, and if being called from a callback, we actually do disable interrupts which is unnecessary. Fix both issues by tracking whenever we get a callback. If that is the case disabling interrupts with event index can be a nop. If not the case disable interrupts. Note: with a split ring there's no explicit "no interrupts" value. For now we write a fixed value so our chance of triggering an interupt is 1/ring size. It's probably better to write something related to the last used index there to reduce the chance even further. For now I'm keeping it simple. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- drivers/virtio/virtio_ring.c | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-)