netdev - Re: qdisc_watchdog_schedule_range

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Message-ID: <a896ad54-297b-c55e-1d34-14ab26949ab6@tarent.de>
Date:   Thu, 13 Oct 2022 01:15:55 +0200 (CEST)
From:   Thorsten Glaser <t.glaser@...ent.de>
To:     Eric Dumazet <eric.dumazet@...il.com>
cc:     netdev@...r.kernel.org
Subject: Re: qdisc_watchdog_schedule_range_ns granularity

On Wed, 12 Oct 2022, Eric Dumazet wrote:

> CONFIG_HIGH_RES_TIMERS=y

It does.

> I don't know how you measure this latency, but net/sched/sch_fq.c has
> instrumentation,

On enqueue I add now+extradelay and save that as enqueue timestamp.
On dequeue I check that now>=timestamp then process the packet,
measuring now-timestamp as queue delay. This is surprisingly higher.

I’ll add some printks as well, to see when I’m called next after
such a watchdog scheduling.

> Under high cpu pressure, it is possible the softirq is delayed,
> because ksoftirqd might compete with user threads.

Is it a good idea to renice these?

Thanks,
//mirabilos
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