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

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Message-ID: <1337707497.3361.233.camel@edumazet-glaptop>
Date:	Tue, 22 May 2012 19:24:57 +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
Subject: Re: Strange latency spikes/TX network stalls on Sun Fire
 X4150(x86) and e1000e

On Tue, 2012-05-22 at 20:11 +0300, Denys Fedoryshchenko wrote:

> By the way, if BQL limit is going lower than MTU, is it considered as a 
> bug?
> If yes, i can try to upload 3.4 to some servers and add condition to 
> WARN_ON if limit < 1500.

There is no problem with BQL limit going lower than the max packet size.

(With TSO it can be 64K)

Remember BQL allows one packet to be sent to device, regardless of its
size.

Next packet might be blocked/stay in Qdisc

If your workload is mostly idle, but sending bursts of 3 packets, then
only one is immediately sent.

Next packets shall wait the TX completion of first packet.



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