netdev - Re: [PATCH] softirq: let ksoftirqd do its job

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Date:   Thu, 01 Sep 2016 05:57:23 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        David Miller <davem@...emloft.net>,
        Rik van Riel <riel@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Hannes Frederic Sowa <hannes@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH] softirq: let ksoftirqd do its job

On Thu, 2016-09-01 at 14:38 +0200, Jesper Dangaard Brouer wrote:

> Correction, on the server-under-test, I'm actually running RHEL7.2
> 
> 
> > How do I verify/check if I have enabled a cpu-cgroup?
> 
> Hannes says I can look in "/proc/self/cgroup"
> 
>  $ cat /proc/self/cgroup
>  7:net_cls:/
>  6:blkio:/
>  5:devices:/
>  4:perf_event:/
>  3:cpu,cpuacct:/
>  2:cpuset:/
>  1:name=systemd:/user.slice/user-1000.slice/session-c1.scope
>  
> And that "/" indicate I've not enabled cgroups, right?
> 

In my experience, I found that times displayed by top are often off for
softirq processing.

Before applying my patch, top shows very small amount of cpu time for
udp_rcv and ksoftirqd/0 , while obviously cpu 0 is completely busy.

Make sure to try latest Linus tree, as I did yesterday, because
apparently things are better than a few weeks back.

BTW, even 'perf top' has sometimes problems showing me cycles spent in
softirq. I need to make sure the cpu processing NIC interrupts also
spend cycles in some user space program to get meaningful results.