netdev - Re: [RFC] New driver API to speed up small packets xmits

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Date:	Fri, 11 May 2007 11:36:25 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	Gagan Arneja <gaagaan@...il.com>
Cc:	Evgeniy Polyakov <johnpol@....mipt.ru>, netdev@...r.kernel.org,
	Rick Jones <rick.jones2@...com>,
	Sridhar Samudrala <sri@...ibm.com>
Subject: Re: [RFC] New driver API to speed up small packets xmits

Hi Gagan,

Gagan Arneja <gaagaan@...il.com> wrote on 05/11/2007 11:27:54 AM:

> >
> > Right, but I am the sole dequeue'r, and on failure, I requeue those
packets
> > to
> > the beginning of the queue (just as it would happen in the regular case
of
> > one
> > packet xmit/failure/requeue).
>
> What about a race between trying to reacquire queue_lock and another
> failed transmit?

That is not possible too. I hold the QDISC_RUNNING bit in dev->state and
am the only sender for this device, so there is no other failed transmit.
Also, on failure of dev_hard_start_xmit, qdisc_restart will spin for the
queue lock (which could be held quickly by enqueuer's), and q->requeue()
skbs to the head of the list.

Thanks,

- KK

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