netdev - RE: Question on "net: allocate skbs on local node"

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Date:	Thu, 07 Apr 2011 08:16:52 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Wei Gu <wei.gu@...csson.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: RE: Question on "net: allocate skbs on local node"

Le jeudi 07 avril 2011 à 07:16 +0200, Eric Dumazet a écrit :
> Le jeudi 07 avril 2011 à 06:58 +0200, Eric Dumazet a écrit :
> > Le jeudi 07 avril 2011 à 10:16 +0800, Wei Gu a écrit :
> > > Hi Eric,
> > > Testing with ixgbe Linux 2.6.38 driver:
> > > We have a little better thruput figure with this driver, but it looks
> > > not scalling at all, I always stressed one CPU core/24.
> > > And when look the perf report for ksoftirqd/24, the most cost function
> > > is still "_raw_spin_unlock_irqstore" and the IRQ/s is huge, it's
> > > somehow conflicts with desgin of NAPI. On linux 2.6.32 while the CPU
> > > was stressed the IRQ will descreased while the NAPI will running much
> > > on the polling mode. I don't know why on 2.6.38 the IRQ was keep
> > > increasing.
> > 
> > 
> > CC netdev and Intel guys, since they said it should not happen (TM)
> > 
> > IF you dont use DCA (make sure ioatdma module is not loaded), how comes
> > alloc_iova() is called at all ?
> > 
> > IF you use DCA, how comes its called, since the same CPU serves a given
> > interrupt ?
> > 
> > 
> 
> But then, maybe you forgot to cpu affine IRQS ?
> 
> High performance routing setup is tricky, since you probably want to
> disable many features that are ON by default : Most machines act as a
> end host.
> 
> 

Please dont send me anymore private mails, I do think the issue you have
is on a setup, not a particular optimization done in network stack.


Copy of your private mail :

> On 2.6.38, I got a lot of "rx_missed_errors" on NIC, which means the
> rx loop was really busy to get packet from the receiving ring. Usually
> in this case it shouldn't exit the softirqs and keep polling in order
> to decrease the initrs.
> 
> On 2.6.32, I can Rx and Tx 2.3Mpps with no packet lost(error on NIC),
> but on 2.6.38 I can only reach 50kpps with a lot of
> "rx_missed_errors", and all the binding cpu core was 100% in SI. I
> don't think there was any optimizations on it.

I hope you understand there is something wrong with your setup ?

50.000 pps on a 64 cpu machine is a bad joke.

We can reach +10.000.000 on a 16 cpus one.



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