From: Thomas Gleixner <tglx@linutronix.de>
To: Eric Dumazet <edumazet@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Chris Mason <clm@fb.com>, Arjan van de Ven <arjan@infradead.org>,
rt@linutronix.de, Rik van Riel <riel@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
George Spelvin <linux@sciencehorizons.net>,
Len Brown <lenb@kernel.org>
Subject: Re: [patch V2 00/20] timer: Refactor the timer wheel
Date: Fri, 17 Jun 2016 15:57:41 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.11.1606171556200.5839@nanos> (raw)
In-Reply-To: <CANn89iKS03PKbT0Acvnn87g5pd8LmaoJQs3zjmByB2zrndENkw@mail.gmail.com>
On Fri, 17 Jun 2016, Eric Dumazet wrote:
> >
> > To achieve this capacity with HZ=1000 without increasing the storage size
> > by another level, we reduced the granularity of the first wheel level from
> > 1ms to 4ms. According to our data, there is no user which relies on that
> > 1ms granularity and 99% of those timers are canceled before expiry.
> >
>
> Ah... This might be a problem for people using small TCP RTO timers in
> datacenters (order of 5 ms)
> (and small delay ack timers as well, in the order of 4 ms)
>
> TCP/pacing uses high resolution timer in sch_fq.c so no problem there.
>
> If we arm a timer for 5 ms, what are the exact consequences ?
The worst case expiry time is 8ms on HZ=1000 as it is on HZ=250
> I fear we might trigger lot more of spurious retransmits.
>
> Or maybe I should read the patch series. I'll take some time today.
Maybe just throw it at such a workload and see what happens :)
Thanks,
tglx
next prev parent reply other threads:[~2016-06-17 13:59 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-17 13:26 [patch V2 00/20] timer: Refactor the timer wheel Thomas Gleixner
2016-06-17 13:26 ` [patch V2 01/20] timer: Make pinned a timer property Thomas Gleixner
2016-06-17 13:26 ` [patch V2 02/20] x86/apic/uv: Initialize timer as pinned Thomas Gleixner
2016-06-17 13:26 ` [patch V2 03/20] x86/mce: " Thomas Gleixner
2016-06-17 13:26 ` [patch V2 05/20] driver/net/ethernet/tile: " Thomas Gleixner
2016-06-21 18:14 ` Peter Zijlstra
2016-06-17 13:26 ` [patch V2 04/20] cpufreq/powernv: " Thomas Gleixner
2016-06-17 13:26 ` [patch V2 06/20] drivers/tty/metag_da: " Thomas Gleixner
2016-06-17 13:26 ` [patch V2 07/20] drivers/tty/mips_ejtag: " Thomas Gleixner
2016-06-17 13:26 ` [patch V2 08/20] net/ipv4/inet: Initialize timers " Thomas Gleixner
2016-06-17 13:26 ` [patch V2 09/20] timer: Remove mod_timer_pinned Thomas Gleixner
2016-06-17 13:26 ` [patch V2 10/20] hlist: Add hlist_is_singular_node() helper Thomas Gleixner
2016-06-17 13:26 ` [patch V2 11/20] timer: Give a few structs and members proper names Thomas Gleixner
2016-06-17 13:26 ` [patch V2 12/20] timer: Switch to a non cascading wheel Thomas Gleixner
2016-06-18 9:55 ` George Spelvin
2016-06-24 10:06 ` Thomas Gleixner
2016-06-17 13:26 ` [patch V2 13/20] timer: Remove slack leftovers Thomas Gleixner
2016-06-17 13:26 ` [patch V2 14/20] timer: Move __run_timers() function Thomas Gleixner
2016-06-17 13:26 ` [patch V2 15/20] timer: Optimize collect timers for NOHZ Thomas Gleixner
2016-06-17 13:26 ` [patch V2 16/20] tick/sched: Remove pointless empty function Thomas Gleixner
2016-06-17 13:26 ` [patch V2 17/20] timer: Forward wheel clock whenever possible Thomas Gleixner
2016-06-17 13:26 ` [patch V2 18/20] timer: Only wake softirq if necessary Thomas Gleixner
2016-06-17 13:26 ` [patch V2 19/20] timer: Split out index calculation Thomas Gleixner
2016-06-17 13:26 ` [patch V2 20/20] timer: Optimization for same expiry time in mod_timer() Thomas Gleixner
2016-06-17 13:48 ` [patch V2 00/20] timer: Refactor the timer wheel Eric Dumazet
2016-06-17 13:57 ` Thomas Gleixner [this message]
2016-06-17 14:25 ` Eric Dumazet
2016-06-20 13:56 ` Thomas Gleixner
2016-06-20 14:46 ` Arjan van de Ven
2016-06-20 14:46 ` Thomas Gleixner
2016-06-20 14:49 ` Arjan van de Ven
2016-06-20 19:03 ` Rik van Riel
2016-06-21 2:48 ` Eric Dumazet
2016-06-17 14:26 ` Arjan van de Ven
2016-06-20 15:05 ` Paul E. McKenney
2016-06-20 15:13 ` Thomas Gleixner
2016-06-20 15:41 ` Paul E. McKenney
2016-06-22 7:37 ` Mike Galbraith
2016-06-22 8:44 ` Thomas Gleixner
2016-06-22 9:06 ` Mike Galbraith
2016-06-22 13:37 ` Mike Galbraith
2016-06-22 10:28 ` [LTP] " Cyril Hrubis
2016-06-23 8:27 ` Thomas Gleixner
2016-06-23 11:47 ` Cyril Hrubis
2016-06-23 13:58 ` George Spelvin
2016-06-23 14:10 ` Thomas Gleixner
2016-06-23 15:11 ` Cyril Hrubis
2016-06-23 15:21 ` Thomas Gleixner
2016-06-23 16:31 ` Cyril Hrubis
2016-06-26 19:00 ` Pavel Machek
2016-06-26 19:21 ` Arjan van de Ven
2016-06-26 20:02 ` Pavel Machek
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