From: Eric Dumazet <eric.dumazet@gmail.com>
To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>,
netdev <netdev@vger.kernel.org>,
Alexander Duyck <aduyck@mirantis.com>,
John Fastabend <john.r.fastabend@intel.com>,
Jamal Hadi Salim <jhs@mojatatu.com>
Subject: Re: [RFC] net: remove busylock
Date: Fri, 20 May 2016 06:47:49 -0700 [thread overview]
Message-ID: <1463752069.18194.294.camel@edumazet-glaptop3.roam.corp.google.com> (raw)
In-Reply-To: <1463749909.18194.291.camel@edumazet-glaptop3.roam.corp.google.com>
On Fri, 2016-05-20 at 06:11 -0700, Eric Dumazet wrote:
> On Fri, 2016-05-20 at 09:29 +0200, Jesper Dangaard Brouer wrote:
>
>
> > The hole idea behind allowing bulk qdisc dequeue, was to mitigate this,
> > by allowing dequeue to do more work, while holding the lock.
> >
> > You mention HTB. Notice HTB does not take advantage of bulk dequeue.
> > Have you tried to enable/allow HTB to bulk dequeue?
> >
>
> Well, __QDISC___STATE_RUNNING means exactly that : one cpu is dequeueing
> many packets from the qdisc and tx them to the device.
>
> It is generic for any kind of qdisc.
>
> HTB bulk dequeue would have to call ->dequeue() mutiple times. If you do
> this while holding qdisc spinlock, you block other cpus from doing
> concurrent ->enqueue(), adding latencies (always the same trade off...)
>
> HTB wont be anytime soon have separate protections for the ->enqueue()
> and the ->dequeue(). Have you looked at this monster ? I did, many
> times...
>
> Note that I am working on a patch to transform __QDISC___STATE_RUNNING
> to a seqcount do that we can grab stats without holding the qdisc lock.
Slide note : __qdisc_run() could probably avoid a __netif_schedule()
when it breaks the loop, if another cpu is busy spinning on qdisc lock.
-> Less (spurious) TX softirq invocations, so less chance to trigger the
infamous ksoftirqd bug we discussed lately.
next prev parent reply other threads:[~2016-05-20 13:47 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-19 17:08 [RFC] net: remove busylock Eric Dumazet
2016-05-19 18:03 ` Alexander Duyck
2016-05-19 18:41 ` Rick Jones
2016-05-19 18:56 ` Eric Dumazet
2016-05-19 19:35 ` Eric Dumazet
2016-05-19 20:39 ` Alexander Duyck
2016-05-20 4:49 ` John Fastabend
2016-05-20 4:56 ` Eric Dumazet
2016-05-20 7:29 ` Jesper Dangaard Brouer
2016-05-20 13:11 ` Eric Dumazet
2016-05-20 13:47 ` Eric Dumazet [this message]
2016-05-20 14:16 ` Eric Dumazet
2016-05-20 17:49 ` Jesper Dangaard Brouer
2016-05-20 21:32 ` Eric Dumazet
2016-05-23 9:50 ` Jesper Dangaard Brouer
2016-05-23 21:24 ` [PATCH net] net_sched: avoid too many hrtimer_start() calls Eric Dumazet
2016-05-24 21:49 ` David Miller
2016-05-24 13:50 ` [RFC] net: remove busylock David Laight
2016-05-24 14:37 ` Eric Dumazet
2016-05-20 16:01 ` John Fastabend
2016-05-19 18:12 ` David Miller
2016-05-19 18:44 ` Eric Dumazet
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