[PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx()
From: Jason Wang <hidden>
Date: 2017-09-22 08:04:00
Also in:
kvm, lkml, netdev
Subsystem:
the rest, virtio host (vhost) · Maintainers:
Linus Torvalds, "Michael S. Tsirkin", Jason Wang, Eugenio Pérez
Possibly related (same subject, not in this thread)
- 2017-09-28 · Re: [PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx() · Jason Wang <hidden>
- 2017-09-28 · Re: [PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx() · Willem de Bruijn <willemdebruijn.kernel@gmail.com>
- 2017-09-27 · Re: [PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx() · "Michael S. Tsirkin" <mst@redhat.com>
- 2017-09-27 · Re: [PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx() · Jason Wang <hidden>
This patch introduces a helper which just increase the used idx. This will be used in pair with vhost_prefetch_desc_indices() by batching code. Signed-off-by: Jason Wang <redacted> --- drivers/vhost/vhost.c | 33 +++++++++++++++++++++++++++++++++ drivers/vhost/vhost.h | 1 + 2 files changed, 34 insertions(+)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 8424166d..6532cda 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c@@ -2178,6 +2178,39 @@ int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len) } EXPORT_SYMBOL_GPL(vhost_add_used); +int vhost_add_used_idx(struct vhost_virtqueue *vq, int n) +{ + u16 old, new; + + old = vq->last_used_idx; + new = (vq->last_used_idx += n); + /* If the driver never bothers to signal in a very long while, + * used index might wrap around. If that happens, invalidate + * signalled_used index we stored. TODO: make sure driver + * signals at least once in 2^16 and remove this. + */ + if (unlikely((u16)(new - vq->signalled_used) < (u16)(new - old))) + vq->signalled_used_valid = false; + + /* Make sure buffer is written before we update index. */ + smp_wmb(); + if (vhost_put_user(vq, cpu_to_vhost16(vq, vq->last_used_idx), + &vq->used->idx)) { + vq_err(vq, "Failed to increment used idx"); + return -EFAULT; + } + if (unlikely(vq->log_used)) { + /* Log used index update. */ + log_write(vq->log_base, + vq->log_addr + offsetof(struct vring_used, idx), + sizeof(vq->used->idx)); + if (vq->log_ctx) + eventfd_signal(vq->log_ctx, 1); + } + return 0; +} +EXPORT_SYMBOL_GPL(vhost_add_used_idx); + static int __vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads, unsigned count)
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 16c2cb6..5dd6c05 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h@@ -199,6 +199,7 @@ int __vhost_get_vq_desc(struct vhost_virtqueue *vq, void vhost_discard_vq_desc(struct vhost_virtqueue *, int n); int vhost_vq_init_access(struct vhost_virtqueue *); +int vhost_add_used_idx(struct vhost_virtqueue *vq, int n); int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len); int vhost_add_used_n(struct vhost_virtqueue *, struct vring_used_elem *heads, unsigned count);
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2.7.4