Michael S. Tsirkin
2017-Sep-26 19:13 UTC
[PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx()
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 at redhat.com> > --- > 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.> -- > 2.7.4
Jason Wang
2017-Sep-27 00:38 UTC
[PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx()
On 2017?09?27? 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 at redhat.com> >> --- >> 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> >> -- >> 2.7.4
Michael S. Tsirkin
2017-Sep-27 22:58 UTC
[PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx()
On Wed, Sep 27, 2017 at 08:38:24AM +0800, Jason Wang wrote:> > > On 2017?09?27? 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 at redhat.com> > > > --- > > > 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. > > ThanksRight 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.> > > > > -- > > > 2.7.4
Apparently Analagous Threads
- [PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx()
- [PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx()
- [PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx()
- [PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx()
- [PATCH net-next RFC 3/5] vhost: introduce vhost_add_used_idx()