Re: [patch] voluntary-preempt-2.6.9-rc1-bk4-R0

From: Lee Revell
Date: Thu Sep 02 2004 - 22:10:16 EST


On Thu, 2004-09-02 at 17:57, Ingo Molnar wrote:
> i've released the -R0 patch:
>
> http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-R0
>
> ontop of:
>
> http://redhat.com/~mingo/voluntary-preempt/diff-bk-040828-2.6.8.1.bz2
>
> i've given up on the netdev_backlog_granularity approach, and as a
> replacement i've modified specific network drivers to return at a safe
> point if softirq preemption is requested.

Makes sense, netdev_max_backlog never made a difference on my system
(via-rhine driver).

If you read that Microsoft paper I posted a link to earlier, they
describe all of the main categories of latencies we have dealt with.
They give special mention to network driver DPCs/softirqs.

The worst offender was a driver that used a DPC/softirq to reset the
card if there was no traffic in 10 seconds, to work around a hardware
lockup bug in some versions. Since the reset path was never designed to
be fast this caused problems. They also mention a similar problem to
the one that still exists with the via-rhine driver (fixed in -mm) where
it uses a DPC to poll for link status.

Lee



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