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Re: route cache DoS testing and softirqs

To: "David S. Miller" <davem@xxxxxxxxxx>
Subject: Re: route cache DoS testing and softirqs
From: Andrea Arcangeli <andrea@xxxxxxx>
Date: Tue, 30 Mar 2004 23:37:42 +0200
Cc: kuznet@xxxxxxxxxxxxx, dipankar@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx, Robert.Olsson@xxxxxxxxxxx, paulmck@xxxxxxxxxx, akpm@xxxxxxxx
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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.

Either that or I'm misreading his numbers, or his stats results are wrong.

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