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Re: route cache DoS testing and softirqs

To: Andrea Arcangeli <andrea@xxxxxxx>
Subject: Re: route cache DoS testing and softirqs
From: Dipankar Sarma <dipankar@xxxxxxxxxx>
Date: Thu, 1 Apr 2004 03:22:14 +0530
Cc: "David S. Miller" <davem@xxxxxxxxxx>, kuznet@xxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx, Robert.Olsson@xxxxxxxxxxx, paulmck@xxxxxxxxxx, akpm@xxxxxxxx
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On Wed, Mar 31, 2004 at 11:31:09PM +0200, Andrea Arcangeli wrote:
> On Thu, Apr 01, 2004 at 02:16:11AM +0530, Dipankar Sarma wrote:
> > I don't do any of this. I just have a separate quiescent state counter
> > for softirq RCU. It is incremented for regular quiescent points
> > like cswitch, userland, idle loop as well as at the completion
> > of each softirq handler. call_rcu_bh() uses its own queues.
> > Everything else works like call_rcu().
> 
> the point is that you want this counter to increase in every cpu quick,
> that's why I was thinking at posting the tasklet, if the counter doesn't
> increase from softirq, you fallback in the grace period length of the
> non-bh rcu.
> 
> maybe the softirq load is so high in all cpus that just the additional
> counter will fix it w/o having to post any additional tasklet (I very
> much hope so but especially with irq binding I don't see it happening,
> however with irq binding you may have a call_rcu_bh_cpuset).  You should
> give it a try and see if it just works.

Ah, forcing CPUs for quiescent state is my last WMD if I have to use it ever :)

Thanks
Dipankar

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