question on netdev_completed_queue()

question on netdev_completed_queue()

[Oliver Neukum]

Hi,

is this function to be called whenever a driver is done with transmitting
data, whether the transmission be successful or not?

	Regards
		Oliver

Re: question on netdev_completed_queue()

[Ben Hutchings]

On Thu, 2012-11-08 at 20:38 +0100, Oliver Neukum wrote:
> Hi,
> 
> is this function to be called whenever a driver is done with transmitting
> data, whether the transmission be successful or not?

Yes, BQL tracks number of packets and bytes in each queue and you have
to tell it about all insertions and removals from the queue.  (Except
that if you flush the queue, you can use netdev_reset_queue() rather
than trying to counting the remaining packets and bytes.)

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

Re: question on netdev_completed_queue()

[Oliver Neukum]

On Thursday 08 November 2012 20:44:13 Ben Hutchings wrote:
> On Thu, 2012-11-08 at 20:38 +0100, Oliver Neukum wrote:
> > Hi,
> > 
> > is this function to be called whenever a driver is done with transmitting
> > data, whether the transmission be successful or not?
> 
> Yes, BQL tracks number of packets and bytes in each queue and you have
> to tell it about all insertions and removals from the queue.  (Except
> that if you flush the queue, you can use netdev_reset_queue() rather
> than trying to counting the remaining packets and bytes.)

Thank you. That opens up the next question. How exact does the count
have to be? Do you care about the exact amount of data or does it just
have to be internally consistent?

	Regards
		Oliver

Re: question on netdev_completed_queue()

[Ben Hutchings]

On Fri, 2012-11-09 at 17:58 +0100, Oliver Neukum wrote:
> On Thursday 08 November 2012 20:44:13 Ben Hutchings wrote:
> > On Thu, 2012-11-08 at 20:38 +0100, Oliver Neukum wrote:
> > > Hi,
> > > 
> > > is this function to be called whenever a driver is done with transmitting
> > > data, whether the transmission be successful or not?
> > 
> > Yes, BQL tracks number of packets and bytes in each queue and you have
> > to tell it about all insertions and removals from the queue.  (Except
> > that if you flush the queue, you can use netdev_reset_queue() rather
> > than trying to counting the remaining packets and bytes.)
> 
> Thank you. That opens up the next question. How exact does the count
> have to be? Do you care about the exact amount of data or does it just
> have to be internally consistent?

The underlying DQL algorithm doesn't care what it's counting.  However
the administrator can adjust the queue limits through sysfs, and they
will expect the numbers to be byte counts.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

Re: question on netdev_completed_queue()

[Eric Dumazet]

On Fri, 2012-11-09 at 17:09 +0000, Ben Hutchings wrote:

> The underlying DQL algorithm doesn't care what it's counting.  However
> the administrator can adjust the queue limits through sysfs, and they
> will expect the numbers to be byte counts.

Yes, skb->len should be a fine approximation, even if slightly wrong for
TSO packets.