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

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Date:	Mon, 21 May 2012 11:06:16 +0300
From:	Denys Fedoryshchenko <denys@...p.net.lb>
To:	Eric Dumazet <eric.dumazet@...il.com>
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 2012-05-21 06:56, Eric Dumazet wrote:
> 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 ?
Not sure it is a lot of time, after all it is 2 x core quad machine, 
should be enough fast for pings.
It will cause stalls on small packets even more seems.

Tested latest git, net-next, still the same, stalls.
hardware latency detector are silent by the way, so there is no 
significant SMI.


---
Denys Fedoryshchenko, Network Engineer, Virtual ISP S.A.L.
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