Add support for used_event feature, and utilize it to reduce the number of interrupts for the guest. Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> --- hw/vhost_net.c | 6 +++++ hw/virtio.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++------ hw/virtio.h | 7 +++++- 3 files changed, 71 insertions(+), 8 deletions(-) diff --git a/hw/vhost_net.c b/hw/vhost_net.c index 7e94f61..18e4653 100644 --- a/hw/vhost_net.c +++ b/hw/vhost_net.c @@ -50,6 +50,9 @@ uint64_t vhost_net_get_features(struct vhost_net *net, uint64_t features) if (!(net->dev.features & (1 << VIRTIO_RING_F_INDIRECT_DESC))) { features &= ~(1 << VIRTIO_RING_F_INDIRECT_DESC); } + if (!(net->dev.features & (1ULL << VIRTIO_RING_F_USED_EVENT_IDX))) { + features &= ~(1ULL << VIRTIO_RING_F_USED_EVENT_IDX); + } if (!(net->dev.features & (1 << VIRTIO_NET_F_MRG_RXBUF))) { features &= ~(1 << VIRTIO_NET_F_MRG_RXBUF); } @@ -65,6 +68,9 @@ void vhost_net_ack_features(struct vhost_net *net, uint64_t features) if (features & (1 << VIRTIO_RING_F_INDIRECT_DESC)) { net->dev.acked_features |= (1 << VIRTIO_RING_F_INDIRECT_DESC); } + if (features & (1ULL << VIRTIO_RING_F_USED_EVENT_IDX)) { + net->dev.acked_features |= (1ULL << VIRTIO_RING_F_USED_EVENT_IDX); + } if (features & (1 << VIRTIO_NET_F_MRG_RXBUF)) { net->dev.acked_features |= (1 << VIRTIO_NET_F_MRG_RXBUF); } diff --git a/hw/virtio.c b/hw/virtio.c index b9acbd4..e459093 100644 --- a/hw/virtio.c +++ b/hw/virtio.c @@ -72,7 +72,14 @@ struct VirtQueue VRing vring; target_phys_addr_t pa; uint16_t last_avail_idx; + /* Last used index value we have signalled on */ + uint16_t signalled_used; + + /* Last used index value we have signalled on */ + bool signalled_used_valid; + int inuse; + uint16_t vector; void (*handle_output)(VirtIODevice *vdev, VirtQueue *vq); VirtIODevice *vdev; @@ -141,6 +148,11 @@ static inline uint16_t vring_avail_ring(VirtQueue *vq, int i) return lduw_phys(pa); } +static inline uint16_t vring_used_event(VirtQueue *vq) +{ + return vring_avail_ring(vq, vq->vring.num); +} + static inline void vring_used_ring_id(VirtQueue *vq, int i, uint32_t val) { target_phys_addr_t pa; @@ -162,11 +174,11 @@ static uint16_t vring_used_idx(VirtQueue *vq) return lduw_phys(pa); } -static inline void vring_used_idx_increment(VirtQueue *vq, uint16_t val) +static inline void vring_used_idx_set(VirtQueue *vq, uint16_t val) { target_phys_addr_t pa; pa = vq->vring.used + offsetof(VRingUsed, idx); - stw_phys(pa, vring_used_idx(vq) + val); + stw_phys(pa, val); } static inline void vring_used_flags_set_bit(VirtQueue *vq, int mask) @@ -234,11 +246,16 @@ void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem, void virtqueue_flush(VirtQueue *vq, unsigned int count) { + uint16_t old, new; /* Make sure buffer is written before we update index. */ wmb(); trace_virtqueue_flush(vq, count); - vring_used_idx_increment(vq, count); + old = vring_used_idx(vq); + new = old + count; + vring_used_idx_set(vq, new); vq->inuse -= count; + if (unlikely((int16_t)(new - vq->signalled_used) < (uint16_t)(new - old))) + vq->signalled_used_valid = false; } void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem, @@ -478,6 +495,8 @@ void virtio_reset(void *opaque) vdev->vq[i].last_avail_idx = 0; vdev->vq[i].pa = 0; vdev->vq[i].vector = VIRTIO_NO_VECTOR; + vdev->vq[i].signalled_used = 0; + vdev->vq[i].signalled_used_valid = false; } } @@ -629,13 +648,45 @@ void virtio_irq(VirtQueue *vq) virtio_notify_vector(vq->vdev, vq->vector); } -void virtio_notify(VirtIODevice *vdev, VirtQueue *vq) +/* Assuming a given event_idx value from the other size, if + * we have just incremented index from old to new_idx, + * should we trigger an event? */ +static inline int vring_need_event(uint16_t event, uint16_t new, uint16_t old) +{ + /* Note: Xen has similar logic for notification hold-off + * in include/xen/interface/io/ring.h with req_event and req_prod + * corresponding to event_idx + 1 and new respectively. + * Note also that req_event and req_prod in Xen start at 1, + * event indexes in virtio start at 0. */ + return (uint16_t)(new - event - 1) < (uint16_t)(new - old); +} + +static bool vring_notify(VirtIODevice *vdev, VirtQueue *vq) { + uint16_t old, new; + bool v; /* Always notify when queue is empty (when feature acknowledge) */ - if ((vring_avail_flags(vq) & VRING_AVAIL_F_NO_INTERRUPT) && - (!(vdev->guest_features & (1 << VIRTIO_F_NOTIFY_ON_EMPTY)) || - (vq->inuse || vring_avail_idx(vq) != vq->last_avail_idx))) + if (((vdev->guest_features & (1 << VIRTIO_F_NOTIFY_ON_EMPTY)) && + !vq->inuse && vring_avail_idx(vq) == vq->last_avail_idx)) { + return true; + } + + if (!(vdev->guest_features & (1ULL << VIRTIO_RING_F_USED_EVENT_IDX))) { + return !(vring_avail_flags(vq) & VRING_AVAIL_F_NO_INTERRUPT); + } + + v = vq->signalled_used_valid; + vq->signalled_used_valid = true; + old = vq->signalled_used; + new = vq->signalled_used = vring_used_idx(vq); + return !v || vring_need_event(vring_used_event(vq), new, old); +} + +void virtio_notify(VirtIODevice *vdev, VirtQueue *vq) +{ + if (!vring_notify(vdev, vq)) { return; + } trace_virtio_notify(vdev, vq); vdev->isr |= 0x01; @@ -732,6 +783,7 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f) vdev->vq[i].vring.num = qemu_get_be32(f); vdev->vq[i].pa = qemu_get_be64(f); qemu_get_be16s(f, &vdev->vq[i].last_avail_idx); + vdev->vq[i].signalled_used_valid = false; if (vdev->vq[i].pa) { uint16_t nheads; diff --git a/hw/virtio.h b/hw/virtio.h index 9517b97..d765946 100644 --- a/hw/virtio.h +++ b/hw/virtio.h @@ -46,6 +46,9 @@ #define VIRTIO_F_NOTIFY_ON_EMPTY 24 /* We support indirect buffer descriptors */ #define VIRTIO_RING_F_INDIRECT_DESC 28 +/* The Guest publishes the used index for which it expects an interrupt + * at the end of the avail ring. Host should ignore the avail->flags field. */ +#define VIRTIO_RING_F_USED_EVENT_IDX 29 /* A guest should never accept this. It implies negotiation is broken. */ #define VIRTIO_F_BAD_FEATURE 30 @@ -213,7 +216,9 @@ void virtio_serial_exit(VirtIODevice *vdev); #define DEFINE_VIRTIO_COMMON_FEATURES(_state, _field) \ DEFINE_PROP_BIT64("indirect_desc", _state, _field, \ - VIRTIO_RING_F_INDIRECT_DESC, true) + VIRTIO_RING_F_INDIRECT_DESC, true), \ + DEFINE_PROP_BIT64("used_event", _state, _field, \ + VIRTIO_RING_F_USED_EVENT_IDX, true) target_phys_addr_t virtio_queue_get_desc_addr(VirtIODevice *vdev, int n); target_phys_addr_t virtio_queue_get_avail_addr(VirtIODevice *vdev, int n); -- 1.7.5.53.gc233e -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html