From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dipankar Sarma Subject: Re: route cache DoS testing and softirqs Date: Tue, 30 Mar 2004 20:13:24 +0530 Sender: netdev-bounce@oss.sgi.com Message-ID: <20040330144324.GA3778@in.ibm.com> References: <20040329184550.GA4540@in.ibm.com> <20040329222926.GF3808@dualathlon.random> Reply-To: dipankar@in.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, netdev@oss.sgi.com, Robert Olsson , "Paul E. McKenney" , Dave Miller , Alexey Kuznetsov , Andrew Morton Return-path: To: Andrea Arcangeli Content-Disposition: inline In-Reply-To: <20040329222926.GF3808@dualathlon.random> Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org On Tue, Mar 30, 2004 at 12:29:26AM +0200, Andrea Arcangeli wrote: > the only real starvation you can claim is in presence of an _hard_irq > flood, not a softirq one. Ingo had some patch for the hardirq > throttling, unfortunately those pathes were mixed with irrelevant > softirq changes, but the hardirq part of these patches was certainly > valid (though in most business environments I imagine if one is under > hardirq attack in the local ethernet, the last worry is probably the > throttling of hardirqs ;) Hmm.. What about firewalls and routers on the internet ? Shouldn't they care ? > So you're simply asking the ksoftirqd offloading to become more > aggressive, and to make the softirq even more scheduler friendly, > something I never had a reason to do yet, since ksoftirqd already > eliminates the starvation issue, and secondly because I did care about > the performance of softirq first (delaying softirqs is derimental for > performance if it happens frequently w/o this kind of flood-load). I > even got a patch for 2.4 doing this kind of changes to the softirqd for > similar reasons on embedded systems where the cpu spent on the softirqs > would been way too much under attack. I had to back it out since it was > causing drop of performance in specweb or something like that and nobody > but the embdedded people needed it. But now here we've a case where it > makes even more sense since the hardirq aren't strictly related to this > load, this load with the rcu-routing-cache is just about letting the > scheduler go together witn an intensive softirq load. So we can try > again with a truly userspace throttling of the softirqs (and in 2.4 I > didn't change the nice from 19 to -20 so maybe this will just work > perfectly). Tried it and it didn't work. I still got dst cache overflows. I will dig out more numbers about what what happened - is ksoftirqd a pig still or we are mostly doing short softirq bursts on the back of a hardirq flood. Thanks Dipankar