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

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Date:	Mon, 21 May 2012 05:56:23 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Denys Fedoryshchenko <denys@...p.net.lb>
Cc:	Tom Herbert <therbert@...gle.com>, netdev@...r.kernel.org,
	e1000-devel@...ts.sourceforge.net, jeffrey.t.kirsher@...el.com,
	jesse.brandeburg@...el.com, davem@...emloft.net
Subject: Re: Strange latency spikes/TX network stalls on Sun Fire
 X4150(x86) and e1000e

On Sun, 2012-05-20 at 22:18 +0300, Denys Fedoryshchenko wrote:
> On 2012-05-20 22:07, Eric Dumazet wrote:
> >
> > You could try latencytop, I am not sure if some obvious things will
> > popup.
> For sure i did. Nothing unusual here, max 5ms latency
> Cause                                                Maximum     
> Percentage
> [__skb_recv_datagram]                               4.1 msec   

Interesting

So your workload is a mix of pings, and receive.

Problem is softirq handler might use a lot of time to complete the
receives, because of TCP stack complexity. And BQL use softirq to
restart the transmits on the same cpu.

tcp_data_queue() can copy the received data directly to user space.
(taking page faults...)

Could you check if net-next behaves the same ?



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