netdev - Re: [PATCH v4 net-next 1/1] net_sched: Introduce skbmod action

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Message-ID: <3a1da0eb-b253-ef9c-8679-0290e670238c@mojatatu.com>
Date:   Mon, 12 Sep 2016 19:02:35 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        xiyou.wangcong@...il.com, daniel@...earbox.net,
        john.r.fastabend@...el.com
Subject: Re: [PATCH v4 net-next 1/1] net_sched: Introduce skbmod action

On 16-09-12 06:26 PM, Eric Dumazet wrote:
> On Mon, 2016-09-12 at 18:14 -0400, Jamal Hadi Salim wrote:
>
>> I noticed some very weird issues when I took that out.
>> Running sufficiently large amount of traffic (ping -f is sufficient)
>> I saw that when i did a dump it took anywhere between 6-15 seconds.
>> With the read_lock in place response was immediate.
>> I can go back and run things to verify - but it was very odd.
>
> This was on uni processor ?
>

It was a VM.

> Looks like typical starvation caused by aggressive softirq.
>

Well, then it is strange that in one case a tc dump of the rule
was immediate and in the other case it was consistent for 5-15
seconds.

> Anyway, I suspect your kernel build has rcu_read_lock() and
> rcu_read_unlock() as NOP ;)
>

Which doesnt give me a good feel if i tested this well ;->

I would like to try again with those two kernels just to
make sure i was not imagining this.

cheers,
jamal