netdev - Re: Strange latency spikes/TX network stalls on Sun Fire X4150(x86) and e1000e

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Message-ID: <1337966295.3347.57.camel@edumazet-glaptop>
Date:	Fri, 25 May 2012 19:18:15 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	Denys Fedoryshchenko <denys@...p.net.lb>, netdev@...r.kernel.org
Subject: Re: Strange latency spikes/TX network stalls on Sun Fire
 X4150(x86) and e1000e

On Fri, 2012-05-25 at 09:59 -0700, Tom Herbert wrote:
> > TX completion has no budget, I am not sure what you mean.
> >
> Right, it's the budget on RX that can be a factor.  TX completion is
> done from the NAPI poll routine, so if RX does not complete the NAPI
> is rescheduled and TX completion is done again for the same HW
> interrupt.
> 
> We need to remove the constraint that netdev_completed can only be
> called once per interrupt...

Not clear where is this constraint in the code.

Under heavy load, we can be in a loop situation, one cpu serving NAPI
for a bunch of devices (no more hardware interrupts are delivered since
we dont re-enable them at all)



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