Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling

[Jason Wang]

On 2017年03月30日 10:33, Michael S. Tsirkin wrote:

On Thu, Mar 30, 2017 at 10:16:15AM +0800, Jason Wang wrote:


On 2017年03月29日 20:07, Michael S. Tsirkin wrote:

On Tue, Mar 21, 2017 at 12:04:47PM +0800, Jason Wang wrote:

For the socket that exports its skb array, we can use lockless polling
to avoid touching spinlock during busy polling.

Signed-off-by: Jason Wang 
---
   drivers/vhost/net.c | 7 +--
   1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 53f09f2..41153a3 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -551,10 +551,13 @@ static int peek_head_len(struct vhost_net_virtqueue *rvq, 
struct sock *sk)
return len;
   }
-static int sk_has_rx_data(struct sock *sk)
+static int sk_has_rx_data(struct vhost_net_virtqueue *rvq, struct sock *sk)
   {
struct socket *sock = sk->sk_socket;
+   if (rvq->rx_array)
+   return !__skb_array_empty(rvq->rx_array);
+
if (sock->ops->peek_len)
return sock->ops->peek_len(sock);

I don't see which patch adds __skb_array_empty.

This is not something new, it was introduced by ad69f35d1dc0a ("skb_array:
array based FIFO for skbs").

Thanks

Same comment about a compiler barrier applies then.


Ok, rethink about this, since skb_array could be resized, using lockless 
version seems wrong.


For the comment of using compiler barrier, caller 
(vhost_net_rx_peek_head_len) uses cpu_relax(). But I haven't figured out 
why a compiler barrier is needed here. Could you please explain?


Thanks




@@ -579,7 +582,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net,
endtime = busy_clock() + vq->busyloop_timeout;
while (vhost_can_busy_poll(>dev, endtime) &&
-  !sk_has_rx_data(sk) &&
+  !sk_has_rx_data(rvq, sk) &&
   vhost_vq_avail_empty(>dev, vq))
cpu_relax();
--
2.7.4

Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling

[Jason Wang]

On 2017年03月30日 10:33, Michael S. Tsirkin wrote:

On Thu, Mar 30, 2017 at 10:16:15AM +0800, Jason Wang wrote:


On 2017年03月29日 20:07, Michael S. Tsirkin wrote:

On Tue, Mar 21, 2017 at 12:04:47PM +0800, Jason Wang wrote:

For the socket that exports its skb array, we can use lockless polling
to avoid touching spinlock during busy polling.

Signed-off-by: Jason Wang 
---
   drivers/vhost/net.c | 7 +--
   1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 53f09f2..41153a3 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -551,10 +551,13 @@ static int peek_head_len(struct vhost_net_virtqueue *rvq, 
struct sock *sk)
return len;
   }
-static int sk_has_rx_data(struct sock *sk)
+static int sk_has_rx_data(struct vhost_net_virtqueue *rvq, struct sock *sk)
   {
struct socket *sock = sk->sk_socket;
+   if (rvq->rx_array)
+   return !__skb_array_empty(rvq->rx_array);
+
if (sock->ops->peek_len)
return sock->ops->peek_len(sock);

I don't see which patch adds __skb_array_empty.

This is not something new, it was introduced by ad69f35d1dc0a ("skb_array:
array based FIFO for skbs").

Thanks

Same comment about a compiler barrier applies then.


Ok, rethink about this, since skb_array could be resized, using lockless 
version seems wrong.


For the comment of using compiler barrier, caller 
(vhost_net_rx_peek_head_len) uses cpu_relax(). But I haven't figured out 
why a compiler barrier is needed here. Could you please explain?


Thanks




@@ -579,7 +582,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net,
endtime = busy_clock() + vq->busyloop_timeout;
while (vhost_can_busy_poll(>dev, endtime) &&
-  !sk_has_rx_data(sk) &&
+  !sk_has_rx_data(rvq, sk) &&
   vhost_vq_avail_empty(>dev, vq))
cpu_relax();
--
2.7.4

Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling

[Michael S. Tsirkin]

On Thu, Mar 30, 2017 at 10:16:15AM +0800, Jason Wang wrote:
> 
> 
> On 2017年03月29日 20:07, Michael S. Tsirkin wrote:
> > On Tue, Mar 21, 2017 at 12:04:47PM +0800, Jason Wang wrote:
> > > For the socket that exports its skb array, we can use lockless polling
> > > to avoid touching spinlock during busy polling.
> > > 
> > > Signed-off-by: Jason Wang 
> > > ---
> > >   drivers/vhost/net.c | 7 +--
> > >   1 file changed, 5 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> > > index 53f09f2..41153a3 100644
> > > --- a/drivers/vhost/net.c
> > > +++ b/drivers/vhost/net.c
> > > @@ -551,10 +551,13 @@ static int peek_head_len(struct vhost_net_virtqueue 
> > > *rvq, struct sock *sk)
> > >   return len;
> > >   }
> > > -static int sk_has_rx_data(struct sock *sk)
> > > +static int sk_has_rx_data(struct vhost_net_virtqueue *rvq, struct sock 
> > > *sk)
> > >   {
> > >   struct socket *sock = sk->sk_socket;
> > > + if (rvq->rx_array)
> > > + return !__skb_array_empty(rvq->rx_array);
> > > +
> > >   if (sock->ops->peek_len)
> > >   return sock->ops->peek_len(sock);
> > I don't see which patch adds __skb_array_empty.
> 
> This is not something new, it was introduced by ad69f35d1dc0a ("skb_array:
> array based FIFO for skbs").
> 
> Thanks

Same comment about a compiler barrier applies then.

> > 
> > > @@ -579,7 +582,7 @@ static int vhost_net_rx_peek_head_len(struct 
> > > vhost_net *net,
> > >   endtime = busy_clock() + vq->busyloop_timeout;
> > >   while (vhost_can_busy_poll(>dev, endtime) &&
> > > -!sk_has_rx_data(sk) &&
> > > +!sk_has_rx_data(rvq, sk) &&
> > >  vhost_vq_avail_empty(>dev, vq))
> > >   cpu_relax();
> > > -- 
> > > 2.7.4

Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling

[Michael S. Tsirkin]

On Thu, Mar 30, 2017 at 10:16:15AM +0800, Jason Wang wrote:
> 
> 
> On 2017年03月29日 20:07, Michael S. Tsirkin wrote:
> > On Tue, Mar 21, 2017 at 12:04:47PM +0800, Jason Wang wrote:
> > > For the socket that exports its skb array, we can use lockless polling
> > > to avoid touching spinlock during busy polling.
> > > 
> > > Signed-off-by: Jason Wang 
> > > ---
> > >   drivers/vhost/net.c | 7 +--
> > >   1 file changed, 5 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> > > index 53f09f2..41153a3 100644
> > > --- a/drivers/vhost/net.c
> > > +++ b/drivers/vhost/net.c
> > > @@ -551,10 +551,13 @@ static int peek_head_len(struct vhost_net_virtqueue 
> > > *rvq, struct sock *sk)
> > >   return len;
> > >   }
> > > -static int sk_has_rx_data(struct sock *sk)
> > > +static int sk_has_rx_data(struct vhost_net_virtqueue *rvq, struct sock 
> > > *sk)
> > >   {
> > >   struct socket *sock = sk->sk_socket;
> > > + if (rvq->rx_array)
> > > + return !__skb_array_empty(rvq->rx_array);
> > > +
> > >   if (sock->ops->peek_len)
> > >   return sock->ops->peek_len(sock);
> > I don't see which patch adds __skb_array_empty.
> 
> This is not something new, it was introduced by ad69f35d1dc0a ("skb_array:
> array based FIFO for skbs").
> 
> Thanks

Same comment about a compiler barrier applies then.

> > 
> > > @@ -579,7 +582,7 @@ static int vhost_net_rx_peek_head_len(struct 
> > > vhost_net *net,
> > >   endtime = busy_clock() + vq->busyloop_timeout;
> > >   while (vhost_can_busy_poll(>dev, endtime) &&
> > > -!sk_has_rx_data(sk) &&
> > > +!sk_has_rx_data(rvq, sk) &&
> > >  vhost_vq_avail_empty(>dev, vq))
> > >   cpu_relax();
> > > -- 
> > > 2.7.4

Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling

[Jason Wang]

On 2017年03月29日 20:07, Michael S. Tsirkin wrote:

On Tue, Mar 21, 2017 at 12:04:47PM +0800, Jason Wang wrote:

For the socket that exports its skb array, we can use lockless polling
to avoid touching spinlock during busy polling.

Signed-off-by: Jason Wang 
---
  drivers/vhost/net.c | 7 +--
  1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 53f09f2..41153a3 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -551,10 +551,13 @@ static int peek_head_len(struct vhost_net_virtqueue *rvq, 
struct sock *sk)
return len;
  }
  
-static int sk_has_rx_data(struct sock *sk)

+static int sk_has_rx_data(struct vhost_net_virtqueue *rvq, struct sock *sk)
  {
struct socket *sock = sk->sk_socket;
  
+	if (rvq->rx_array)

+   return !__skb_array_empty(rvq->rx_array);
+
if (sock->ops->peek_len)
return sock->ops->peek_len(sock);
  

I don't see which patch adds __skb_array_empty.


This is not something new, it was introduced by ad69f35d1dc0a 
("skb_array: array based FIFO for skbs").


Thanks




@@ -579,7 +582,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net,
endtime = busy_clock() + vq->busyloop_timeout;
  
  		while (vhost_can_busy_poll(>dev, endtime) &&

-  !sk_has_rx_data(sk) &&
+  !sk_has_rx_data(rvq, sk) &&
   vhost_vq_avail_empty(>dev, vq))
cpu_relax();
  
--

2.7.4

Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling

[Jason Wang]

On 2017年03月29日 20:07, Michael S. Tsirkin wrote:

On Tue, Mar 21, 2017 at 12:04:47PM +0800, Jason Wang wrote:

For the socket that exports its skb array, we can use lockless polling
to avoid touching spinlock during busy polling.

Signed-off-by: Jason Wang 
---
  drivers/vhost/net.c | 7 +--
  1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 53f09f2..41153a3 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -551,10 +551,13 @@ static int peek_head_len(struct vhost_net_virtqueue *rvq, 
struct sock *sk)
return len;
  }
  
-static int sk_has_rx_data(struct sock *sk)

+static int sk_has_rx_data(struct vhost_net_virtqueue *rvq, struct sock *sk)
  {
struct socket *sock = sk->sk_socket;
  
+	if (rvq->rx_array)

+   return !__skb_array_empty(rvq->rx_array);
+
if (sock->ops->peek_len)
return sock->ops->peek_len(sock);
  

I don't see which patch adds __skb_array_empty.


This is not something new, it was introduced by ad69f35d1dc0a 
("skb_array: array based FIFO for skbs").


Thanks




@@ -579,7 +582,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net,
endtime = busy_clock() + vq->busyloop_timeout;
  
  		while (vhost_can_busy_poll(>dev, endtime) &&

-  !sk_has_rx_data(sk) &&
+  !sk_has_rx_data(rvq, sk) &&
   vhost_vq_avail_empty(>dev, vq))
cpu_relax();
  
--

2.7.4

Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling

[Michael S. Tsirkin]

On Tue, Mar 21, 2017 at 12:04:47PM +0800, Jason Wang wrote:
> For the socket that exports its skb array, we can use lockless polling
> to avoid touching spinlock during busy polling.
> 
> Signed-off-by: Jason Wang 
> ---
>  drivers/vhost/net.c | 7 +--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 53f09f2..41153a3 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -551,10 +551,13 @@ static int peek_head_len(struct vhost_net_virtqueue 
> *rvq, struct sock *sk)
>   return len;
>  }
>  
> -static int sk_has_rx_data(struct sock *sk)
> +static int sk_has_rx_data(struct vhost_net_virtqueue *rvq, struct sock *sk)
>  {
>   struct socket *sock = sk->sk_socket;
>  
> + if (rvq->rx_array)
> + return !__skb_array_empty(rvq->rx_array);
> +
>   if (sock->ops->peek_len)
>   return sock->ops->peek_len(sock);
>  

I don't see which patch adds __skb_array_empty.

> @@ -579,7 +582,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net 
> *net,
>   endtime = busy_clock() + vq->busyloop_timeout;
>  
>   while (vhost_can_busy_poll(>dev, endtime) &&
> -!sk_has_rx_data(sk) &&
> +!sk_has_rx_data(rvq, sk) &&
>  vhost_vq_avail_empty(>dev, vq))
>   cpu_relax();
>  
> -- 
> 2.7.4

Re: [PATCH net-next 8/8] vhost_net: use lockless peeking for skb array during busy polling

[Michael S. Tsirkin]

On Tue, Mar 21, 2017 at 12:04:47PM +0800, Jason Wang wrote:
> For the socket that exports its skb array, we can use lockless polling
> to avoid touching spinlock during busy polling.
> 
> Signed-off-by: Jason Wang 
> ---
>  drivers/vhost/net.c | 7 +--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 53f09f2..41153a3 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -551,10 +551,13 @@ static int peek_head_len(struct vhost_net_virtqueue 
> *rvq, struct sock *sk)
>   return len;
>  }
>  
> -static int sk_has_rx_data(struct sock *sk)
> +static int sk_has_rx_data(struct vhost_net_virtqueue *rvq, struct sock *sk)
>  {
>   struct socket *sock = sk->sk_socket;
>  
> + if (rvq->rx_array)
> + return !__skb_array_empty(rvq->rx_array);
> +
>   if (sock->ops->peek_len)
>   return sock->ops->peek_len(sock);
>  

I don't see which patch adds __skb_array_empty.

> @@ -579,7 +582,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net 
> *net,
>   endtime = busy_clock() + vq->busyloop_timeout;
>  
>   while (vhost_can_busy_poll(>dev, endtime) &&
> -!sk_has_rx_data(sk) &&
> +!sk_has_rx_data(rvq, sk) &&
>  vhost_vq_avail_empty(>dev, vq))
>   cpu_relax();
>  
> -- 
> 2.7.4