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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: Wed, 31 Mar 2004 22:40:24 +0530
Cc: "David S. Miller" <davem@xxxxxxxxxx>, kuznet@xxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx, Robert.Olsson@xxxxxxxxxxx, paulmck@xxxxxxxxxx, akpm@xxxxxxxx
In-reply-to: <20040330213742.GL3808@dualathlon.random>
References: <20040329222926.GF3808@dualathlon.random> <200403302005.AAA00466@yakov.inr.ac.ru> <20040330211450.GI3808@dualathlon.random> <20040330133000.098761e2.davem@redhat.com> <20040330213742.GL3808@dualathlon.random>
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On Tue, Mar 30, 2004 at 11:37:42PM +0200, Andrea Arcangeli wrote:
> On Tue, Mar 30, 2004 at 01:30:00PM -0800, David S. Miller wrote:
> > On Tue, 30 Mar 2004 23:14:50 +0200
> > Andrea Arcangeli <andrea@xxxxxxx> wrote:
> > 
> > > > There are no hardirqs in the case under investigation, remember?
> > > 
> > > no hardirqs? there must be tons of hardirqs if ksoftirqd never runs.
> > 
> > NAPI should be kicking in for this workload, and I know for a fact it is
> > for Robert's case.  There should only be a few thousand hard irqs per
> > second.
> > 
> > Until the RX ring is depleted the device's hardirqs will not be re-
> > enabled.
> 
> then Dipankar is reproducing with a workload that is completely
> different. I've only seen the emails from Dipankar so I couldn't know it
> was a NAPI load.
> 
> He posted these numbers:
> 
>       softirq_count, ksoftirqd_count and other_softirq_count shows -
>       
>       CPU 0 : 638240  554     637686
>       CPU 1 : 102316  1       102315
>       CPU 2 : 675696  557     675139
>       CPU 3 : 102305  0       102305
> 
> that means nothing runs in ksoftirqd for Dipankar, so he cannot be using
> NAPI.

And I am not. I am still on 2.6.0 and there seems to be no NAPI support
for the e100 there. Should I try 2.6.4 where e100 has NAPI support ?

Anyway, even without softirqs on the back of hardirqs, there are
other ways of softirq overload as seen in Robert's setup.

Thanks
Dipankar

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