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Message-ID: <2b195a93-a88b-33c2-661a-85fa8513c063@gmail.com> Date: Wed, 12 Oct 2022 16:32:56 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Thorsten Glaser <t.glaser@...ent.de> Cc: netdev@...r.kernel.org Subject: Re: qdisc_watchdog_schedule_range_ns granularity On 10/12/22 16:15, Thorsten Glaser wrote: > 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. When packets are eligible, the qdisc itself can be stopped if NIC is full (or BQL triggers) net/sched/sch_fq.c is not using the skb tstamp which could very well be in the past, but an internal variable (q->time_next_delayed_flow) > > 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? Depends if you want to starve user thread(s) under flood/attack, I guess you can try. > > Thanks, > //mirabilos
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