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Re: route cache DoS testing and softirqs

To: dipankar@xxxxxxxxxx
Subject: Re: route cache DoS testing and softirqs
From: kuznet@xxxxxxxxxxxxx
Date: Thu, 1 Apr 2004 10:00:36 +0400 (MSD)
Cc: andrea@xxxxxxx (Andrea Arcangeli), linux-kernel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx, Robert.Olsson@xxxxxxxxxxx, paulmck@xxxxxxxxxx (Paul E. McKenney), davem@xxxxxxxxxx (Dave Miller), akpm@xxxxxxxx (Andrew Morton)
In-reply-to: <20040330202820.GA3956@xxxxxxxxxx> from "Dipankar Sarma" at Mar 31, 2004 01:58:21 AM
Sender: netdev-bounce@xxxxxxxxxxx
Hello!

> > We had one full solution for this issue not changing anything
> > in scheduler/softirq relationship: to run rcu task for the things
> > sort of dst cache not from process context, but essentially as part
> > of do_softirq(). Simple, stupid and apparently solves new problems
> > which rcu created.
> 
> Can you be a little bit more specific about this solution ?

It is about that your suggestion, which you outlined below :-)

> as indicated by my earlier experiments. We have potential fixes
> for RCU through a call_rcu_bh() interface where completion of a
> softirq handler is a quiescent state. I am working on forward porting
> that old patch from our discussion last year and testing in my
> environment. That should increase the number of quiescent state
> points significantly and hopefully reduce the grace period significantly.
> But this does nothing to help userland starvation.

Alexey

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