Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-Q5

Lee Revell
2004-08-31T23:07:53Z

On Tue, 2004-08-31 at 02:53, Ingo Molnar wrote:
> > >
> > > http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-Q5
>
> ok. It seems the random driver is _mostly_ in shape latency-wise, except
> the IP rekeying visible in the above trace. To solve this problem, could
> you try the patch below, ontop of -Q5? It moves the random seed
> generation outside of the spinlock - AFAICS the spinlock is only needed
> to protect the IP sequence counter itself.

This solves the problem with the random driver. The worst latencies I
am seeing are in netif_receive_skb(). With netdev_max_backlog set to 8,
the worst is about 160 usecs:

http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q5#/var/www/2.6.9-rc1-Q5/trace2.txt
http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q5#/var/www/2.6.9-rc1-Q5/trace3.txt

Setting netdev_max_backlog to 1 has no effect:

http://krustophenia.net/testresults.php?dataset=2.6.9-rc1-Q5#/var/www/2.6.9-rc1-Q5/trace4.txt

I would expect this one to scale with CPU speed, so this is pretty good
considering my relatively underpowered system. I would imagine on a
fast UP system you would not see any latencies worse than 100 usecs.

Lee