netdev - Re: tx queue hashing hot-spots and poor performance (multiq, ixgbe)

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Message-ID: <49FAA570.2040802@cosmosbay.com>
Date:	Fri, 01 May 2009 09:32:00 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Andrew Dickinson <andrew@...dna.net>
CC:	David Miller <davem@...emloft.net>, jelaas@...il.com,
	netdev@...r.kernel.org
Subject: Re: tx queue hashing hot-spots and poor performance (multiq, ixgbe)

Andrew Dickinson a écrit :
> Adding a bit more info...
> 
> I should add, the other 4 ksoftirqd tasklets _are_ running, they're
> just not busy. (In case that wasn't clear...)
> 
> Also of note, I rebooted the box (after recompiling with NUMA off).
> This time when I push traffic through, only the even-ksoftirqd's were
> busy..  I then tweaked some of the ring settings via ethtool and
> suddenly the odd-ksoftirqd's became busy (and the even ones went
> idle).
> 
> Thoughts?  Suggestions?  driver issue?  I'm at 2.6.30-rc3.
> 
> (BTW, I'm under the assumption that since only 4 (of 8) ksoftirqd's
> are busy that I still have room to make this box go faster).

I dont see the point here. ksoftirqd is running only if too much
work has to be done in softirq context. Which should be your case
since you want to saturate cpus with network load.

You could try to change /proc/sys/net/core/netdev_budget if you really
want to trigger ksoftirqd sooner or later, but it wont fundamentally
change routing performance.

If you believe box is loosing frames because cpu are saturated, please
post some oprofile results.


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