[PATCH v2 net-next] net: Functions to report space available in device TX queues

[PATCH v2 net-next] net: Functions to report space available in device TX queues

[Tom Herbert]

This patch adds netdev_tx_avail_queue and netdev_avail_queue which are
used to report number of bytes available in transmit queues per BQL. The
functions call dql_avail which returns BQL limit minus number of
inflight bytes. These functions can be called without txlock, for
instance to ascertain how much data should be dequeued from a qdisc in
a batch. When called without the tx_lock, the result is technically a
hint, subsequently when the tx_lock is done for a transmit it is
possible the availability has changed (for example a transmit
completion may have freed up more space in the queue or changed the
limit).

Signed-off-by: Tom Herbert <therbert@google.com>
---
 include/linux/netdevice.h | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 0fac884..bdf6c85 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2544,6 +2544,30 @@ static inline void netdev_completed_queue(struct net_device *dev,
 	netdev_tx_completed_queue(netdev_get_tx_queue(dev, 0), pkts, bytes);
 }
 
+static inline int netdev_tx_avail_queue(struct netdev_queue *dev_queue)
+{
+#ifdef CONFIG_BQL
+	return dql_avail(&dev_queue->dql);
+#else
+	return DQL_MAX_LIMIT;
+#endif
+}
+
+/**
+ *	netdev_avail_queue - report how much space is availble for xmit
+ *	@dev: network device
+ *
+ *	Report the amount of space available in the TX queue in terms of
+ *	number of bytes. This returns the number of bytes avaiable per
+ *	DQL. This function may be called without taking the txlock on
+ *	the device, however in that case the result should be taken as
+ *	a (strong) hint.
+ */
+static inline int netdev_avail_queue(struct net_device *dev)
+{
+	return netdev_tx_avail_queue(netdev_get_tx_queue(dev, 0));
+}
+
 static inline void netdev_tx_reset_queue(struct netdev_queue *q)
 {
 #ifdef CONFIG_BQL
@@ -2559,9 +2583,9 @@ static inline void netdev_tx_reset_queue(struct netdev_queue *q)
  * 	Reset the bytes and packet count of a network device and clear the
  * 	software flow control OFF bit for this network device
  */
-static inline void netdev_reset_queue(struct net_device *dev_queue)
+static inline void netdev_reset_queue(struct net_device *dev)
 {
-	netdev_tx_reset_queue(netdev_get_tx_queue(dev_queue, 0));
+	netdev_tx_reset_queue(netdev_get_tx_queue(dev, 0));
 }
 
 /**
-- 
2.1.0.rc2.206.gedb03e5

Re: [PATCH v2 net-next] net: Functions to report space available in device TX queues

[David Miller]

From: Tom Herbert <therbert@google.com>
Date: Mon, 25 Aug 2014 08:27:56 -0700 (PDT)

> This patch adds netdev_tx_avail_queue and netdev_avail_queue which are
> used to report number of bytes available in transmit queues per BQL. The
> functions call dql_avail which returns BQL limit minus number of
> inflight bytes. These functions can be called without txlock, for
> instance to ascertain how much data should be dequeued from a qdisc in
> a batch. When called without the tx_lock, the result is technically a
> hint, subsequently when the tx_lock is done for a transmit it is
> possible the availability has changed (for example a transmit
> completion may have freed up more space in the queue or changed the
> limit).
> 
> Signed-off-by: Tom Herbert <therbert@google.com>

Ok this looks fine, but could you please resubmit this alongside
the first use case?

Thanks.

Re: [PATCH v2 net-next] net: Functions to report space available in device TX queues

[Tom Herbert]

On Mon, Aug 25, 2014 at 5:33 PM, David Miller <davem@davemloft.net> wrote:
> From: Tom Herbert <therbert@google.com>
> Date: Mon, 25 Aug 2014 08:27:56 -0700 (PDT)
>
>> This patch adds netdev_tx_avail_queue and netdev_avail_queue which are
>> used to report number of bytes available in transmit queues per BQL. The
>> functions call dql_avail which returns BQL limit minus number of
>> inflight bytes. These functions can be called without txlock, for
>> instance to ascertain how much data should be dequeued from a qdisc in
>> a batch. When called without the tx_lock, the result is technically a
>> hint, subsequently when the tx_lock is done for a transmit it is
>> possible the availability has changed (for example a transmit
>> completion may have freed up more space in the queue or changed the
>> limit).
>>
>> Signed-off-by: Tom Herbert <therbert@google.com>
>
> Ok this looks fine, but could you please resubmit this alongside
> the first use case?
>
It should be called when determining the best size for a transmit
batch, e.g. how many bytes to dequeue from qdisc on wakeup.

> Thanks.

Re: [PATCH v2 net-next] net: Functions to report space available in device TX queues

[Jesper Dangaard Brouer]

On Mon, 25 Aug 2014 08:27:56 -0700 (PDT)
Tom Herbert <therbert@google.com> wrote:

> This patch adds netdev_tx_avail_queue and netdev_avail_queue which are
> used to report number of bytes available in transmit queues per BQL. The
> functions call dql_avail which returns BQL limit minus number of
> inflight bytes. These functions can be called without txlock, for
> instance to ascertain how much data should be dequeued from a qdisc in
> a batch. When called without the tx_lock, the result is technically a
> hint, subsequently when the tx_lock is done for a transmit it is
> possible the availability has changed (for example a transmit
> completion may have freed up more space in the queue or changed the
> limit).
> 
> Signed-off-by: Tom Herbert <therbert@google.com>
> ---
>  include/linux/netdevice.h | 28 ++++++++++++++++++++++++++--
>  1 file changed, 26 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 0fac884..bdf6c85 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -2544,6 +2544,30 @@ static inline void netdev_completed_queue(struct net_device *dev,
>  	netdev_tx_completed_queue(netdev_get_tx_queue(dev, 0), pkts, bytes);
>  }
>  
> +static inline int netdev_tx_avail_queue(struct netdev_queue *dev_queue)
> +{
> +#ifdef CONFIG_BQL
> +	return dql_avail(&dev_queue->dql);
> +#else
> +	return DQL_MAX_LIMIT;
> +#endif
> +}
> +
> +/**
> + *	netdev_avail_queue - report how much space is availble for xmit
> + *	@dev: network device
> + *
> + *	Report the amount of space available in the TX queue in terms of
> + *	number of bytes. This returns the number of bytes avaiable per
> + *	DQL. This function may be called without taking the txlock on
> + *	the device, however in that case the result should be taken as
> + *	a (strong) hint.
> + */
> +static inline int netdev_avail_queue(struct net_device *dev)
> +{
> +	return netdev_tx_avail_queue(netdev_get_tx_queue(dev, 0));
> +}
> +

How can this work, when you are always passing 0 to: netdev_get_tx_queue(dev, 0)
???

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer

Re: [PATCH v2 net-next] net: Functions to report space available in device TX queues

[Eric Dumazet]

On Wed, 2014-09-03 at 15:20 +0200, Jesper Dangaard Brouer wrote:
> On Mon, 25 Aug 2014 08:27:56 -0700 (PDT)
> Tom Herbert <therbert@google.com> wrote:
> 
> > This patch adds netdev_tx_avail_queue and netdev_avail_queue which are
> > used to report number of bytes available in transmit queues per BQL. The
> > functions call dql_avail which returns BQL limit minus number of
> > inflight bytes. These functions can be called without txlock, for
> > instance to ascertain how much data should be dequeued from a qdisc in
> > a batch. When called without the tx_lock, the result is technically a
> > hint, subsequently when the tx_lock is done for a transmit it is
> > possible the availability has changed (for example a transmit
> > completion may have freed up more space in the queue or changed the
> > limit).
> > 
> > Signed-off-by: Tom Herbert <therbert@google.com>
> > ---
> >  include/linux/netdevice.h | 28 ++++++++++++++++++++++++++--
> >  1 file changed, 26 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index 0fac884..bdf6c85 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -2544,6 +2544,30 @@ static inline void netdev_completed_queue(struct net_device *dev,
> >  	netdev_tx_completed_queue(netdev_get_tx_queue(dev, 0), pkts, bytes);
> >  }
> >  
> > +static inline int netdev_tx_avail_queue(struct netdev_queue *dev_queue)
> > +{
> > +#ifdef CONFIG_BQL
> > +	return dql_avail(&dev_queue->dql);
> > +#else
> > +	return DQL_MAX_LIMIT;
> > +#endif
> > +}
> > +
> > +/**
> > + *	netdev_avail_queue - report how much space is availble for xmit
> > + *	@dev: network device
> > + *
> > + *	Report the amount of space available in the TX queue in terms of
> > + *	number of bytes. This returns the number of bytes avaiable per
> > + *	DQL. This function may be called without taking the txlock on
> > + *	the device, however in that case the result should be taken as
> > + *	a (strong) hint.
> > + */
> > +static inline int netdev_avail_queue(struct net_device *dev)
> > +{
> > +	return netdev_tx_avail_queue(netdev_get_tx_queue(dev, 0));
> > +}
> > +
> 
> How can this work, when you are always passing 0 to: netdev_get_tx_queue(dev, 0)
> ???
> 

This is the helper for drivers having a single TX queue.

Re: [PATCH v2 net-next] net: Functions to report space available in device TX queues

[Jesper Dangaard Brouer]

On Wed, 03 Sep 2014 06:41:57 -0700
Eric Dumazet <eric.dumazet@gmail.com> wrote:

> On Wed, 2014-09-03 at 15:20 +0200, Jesper Dangaard Brouer wrote:
> > On Mon, 25 Aug 2014 08:27:56 -0700 (PDT)
> > Tom Herbert <therbert@google.com> wrote:
> > 
> > > This patch adds netdev_tx_avail_queue and netdev_avail_queue which are
> > > used to report number of bytes available in transmit queues per BQL. The
> > > functions call dql_avail which returns BQL limit minus number of
> > > inflight bytes. These functions can be called without txlock, for
> > > instance to ascertain how much data should be dequeued from a qdisc in
> > > a batch. When called without the tx_lock, the result is technically a
> > > hint, subsequently when the tx_lock is done for a transmit it is
> > > possible the availability has changed (for example a transmit
> > > completion may have freed up more space in the queue or changed the
> > > limit).
> > > 
> > > Signed-off-by: Tom Herbert <therbert@google.com>
> > > ---
> > >  include/linux/netdevice.h | 28 ++++++++++++++++++++++++++--
> > >  1 file changed, 26 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > > index 0fac884..bdf6c85 100644
> > > --- a/include/linux/netdevice.h
> > > +++ b/include/linux/netdevice.h
> > > @@ -2544,6 +2544,30 @@ static inline void netdev_completed_queue(struct net_device *dev,
> > >  	netdev_tx_completed_queue(netdev_get_tx_queue(dev, 0), pkts, bytes);
> > >  }
> > >  
> > > +static inline int netdev_tx_avail_queue(struct netdev_queue *dev_queue)
> > > +{
> > > +#ifdef CONFIG_BQL
> > > +	return dql_avail(&dev_queue->dql);
> > > +#else
> > > +	return DQL_MAX_LIMIT;
> > > +#endif
> > > +}
> > > +
> > > +/**
> > > + *	netdev_avail_queue - report how much space is availble for xmit
> > > + *	@dev: network device
> > > + *
> > > + *	Report the amount of space available in the TX queue in terms of
> > > + *	number of bytes. This returns the number of bytes avaiable per
> > > + *	DQL. This function may be called without taking the txlock on
> > > + *	the device, however in that case the result should be taken as
> > > + *	a (strong) hint.
> > > + */
> > > +static inline int netdev_avail_queue(struct net_device *dev)
> > > +{
> > > +	return netdev_tx_avail_queue(netdev_get_tx_queue(dev, 0));
> > > +}
> > > +
> > 
> > How can this work, when you are always passing 0 to: netdev_get_tx_queue(dev, 0)
> > ???
> > 
> 
> This is the helper for drivers having a single TX queue.

Okay, so I should use:
 bytelimit = netdev_tx_avail_queue(txq);



-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer