On 2017年09月28日 06:58, Michael S. Tsirkin wrote:
On Wed, Sep 27, 2017 at 08:38:24AM +0800, Jason Wang wrote:
On 2017年09月27日 03:13, Michael S. Tsirkin wrote:
On Fri, Sep 22, 2017 at 04:02:33PM +0800, Jason Wang wrote:
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<jasowang@xxxxxxxxxx>
---
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);
Please change the API to hide the fact that there's an index that needs
to be updated.
In fact, an interesting optimization on top is just call
vhost_add_used_idx(vq, n) instead of n vhost_add_used_idx(vq, 1). That's the
reason I leave n in the API.
Thanks
Right but you could increment some internal counter in the vq
structure then update the used index using some api
with a generic name, e.g. add_used_complete or something like this.
Right, I see.
Thanks
