From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Rik van Riel <riel@redhat.com>
Cc: Jouni Malinen <jkmalinen@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Chris Mason <clm@fb.com>, Arjan van de Ven <arjan@infradead.org>,
rt@linutronix.de, George Spelvin <linux@sciencehorizons.net>,
Len Brown <lenb@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Eric Dumazet <edumazet@google.com>
Subject: Re: [patch 4 14/22] timer: Switch to a non cascading wheel
Date: Fri, 12 Aug 2016 12:14:11 -0700 [thread overview]
Message-ID: <20160812191411.GA12616@linux.vnet.ibm.com> (raw)
In-Reply-To: <1471024216.32433.5.camel@redhat.com>
On Fri, Aug 12, 2016 at 01:50:16PM -0400, Rik van Riel wrote:
> On Thu, 2016-08-11 at 18:21 +0300, Jouni Malinen wrote:
> > On Mon, Jul 4, 2016 at 12:50 PM, Thomas Gleixner <tglx@linutronix.de>
> > wrote:
> > > The current timer wheel has some drawbacks:
> > ...
> >
> > It looks like this change (commit
> > 500462a9de657f86edaa102f8ab6bff7f7e43fc2 in linux.git) breaks one of
> > the automated test cases I'm using to test hostapd and wpa_supplicant
> > with mac80211_hwsim from the kernel. I'm not sure what exactly causes
> > this (did not really expect git bisect to point to timers..), but
> > this
> > seems to be very reproducible for me under kvm (though, this
> > apparently did not happen on another device, so I'm not completely
> > sure what it is needed to reproduce) with the ap_wps_er_http_proto
> > test cases failing to connect 20 TCP stream sockets to a server on
> > the
> > localhost. The client side is a python test script and the server is
> > hostapd. The failure shows up with about the 13th of those socket
> > connects failing while all others (both before and after this failed
> > one) going through.
> >
> > Would you happen to have any idea why this commit has such a
> > difference in behavior?
>
> I have a vague hypothesis, more of a question actually.
>
> How does the new timer wheel code handle lost timer ticks?
>
> If a KVM guest does not run for a while, because the host
> is scheduling something else, the guest generally only gets
> one timer tick after the guest is scheduled back in.
>
> If there are multiple lost ticks, they will remain lost.
>
> Could that cause the new timer wheel code to skip over
> timer buckets occasionally, or is this hypothesis bunk?
FWIW, I do appear to be seeing more lost wakeups on current mainline
than on v4.7, but not enough of a difference to get a reliable bisction
in reasonable time.
Thanx, Paul
next prev parent reply other threads:[~2016-08-12 19:14 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-04 9:50 [patch 4 00/22] timer: Refactor the timer wheel Thomas Gleixner
2016-07-04 9:50 ` [patch 4 01/22] timer: Make pinned a timer property Thomas Gleixner
2016-07-07 8:39 ` [tip:timers/core] timers: Make 'pinned' " tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 02/22] x86/apic/uv: Initialize timer as pinned Thomas Gleixner
2016-07-07 8:40 ` [tip:timers/core] timers, x86/apic/uv: Initialize the UV heartbeat " tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 03/22] x86/mce: Initialize " Thomas Gleixner
2016-07-07 8:40 ` [tip:timers/core] timers, x86/mce: Initialize MCE restart " tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 04/22] cpufreq/powernv: Initialize " Thomas Gleixner
2016-07-07 8:41 ` [tip:timers/core] timers, cpufreq/powernv: Initialize the gpstate " tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 05/22] driver/net/ethernet/tile: Initialize " Thomas Gleixner
2016-07-07 8:41 ` [tip:timers/core] timers, driver/net/ethernet/tile: Initialize the egress " tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 06/22] drivers/tty/metag_da: Initialize " Thomas Gleixner
2016-07-07 8:42 ` [tip:timers/core] timers, drivers/tty/metag_da: Initialize the poll " tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 07/22] drivers/tty/mips_ejtag: Initialize " Thomas Gleixner
2016-07-07 8:42 ` [tip:timers/core] timers, drivers/tty/mips_ejtag: Initialize the poll " tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 08/22] net/ipv4/inet: Initialize timers " Thomas Gleixner
2016-07-07 8:43 ` [tip:timers/core] timers, net/ipv4/inet: Initialize connection request " tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 09/22] timer: Remove mod_timer_pinned Thomas Gleixner
2016-07-07 8:43 ` [tip:timers/core] timers: Remove the deprecated mod_timer_pinned() API tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 10/22] signal: Use hrtimer for sigtimedwait Thomas Gleixner
2016-07-07 8:43 ` [tip:timers/core] signals: Use hrtimer for sigtimedwait() tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 11/22] hlist: Add hlist_is_singular_node() helper Thomas Gleixner
2016-07-07 8:44 ` [tip:timers/core] " tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 12/22] timer: Give a few structs and members proper names Thomas Gleixner
2016-07-07 8:44 ` [tip:timers/core] timers: " tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 13/22] timer: Reduce the CPU index space to 256k Thomas Gleixner
2016-07-07 8:45 ` [tip:timers/core] timers: " tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 14/22] timer: Switch to a non cascading wheel Thomas Gleixner
2016-07-07 8:45 ` [tip:timers/core] timers: Switch to a non-cascading wheel tip-bot for Thomas Gleixner
2016-08-11 15:21 ` [patch 4 14/22] timer: Switch to a non cascading wheel Jouni Malinen
2016-08-11 20:25 ` [PREEMPT-RT] " rcochran
2016-08-13 9:12 ` Jouni Malinen
2016-08-16 9:46 ` Richard Cochran
2016-08-16 14:35 ` Eric Dumazet
2016-08-17 9:05 ` Jouni Malinen
2016-08-17 9:23 ` rcochran
2016-08-12 17:50 ` Rik van Riel
2016-08-12 19:14 ` Paul E. McKenney [this message]
2016-08-16 8:55 ` Richard Cochran
2016-08-16 7:57 ` Richard Cochran
2016-07-04 9:50 ` [patch 4 15/22] timer: Remove slack leftovers Thomas Gleixner
2016-07-07 8:46 ` [tip:timers/core] timers: Remove set_timer_slack() leftovers tip-bot for Thomas Gleixner
2016-07-22 11:31 ` [patch 4 15/22] timer: Remove slack leftovers Jason A. Donenfeld
2016-07-22 13:04 ` Thomas Gleixner
2016-07-22 15:18 ` Jason A. Donenfeld
2016-07-22 22:54 ` Jason A. Donenfeld
2016-07-04 9:50 ` [patch 4 16/22] timer: Move __run_timers() function Thomas Gleixner
2016-07-07 8:46 ` [tip:timers/core] timers: " tip-bot for Anna-Maria Gleixner
2016-07-04 9:50 ` [patch 4 17/22] timer: Optimize collect timers for NOHZ Thomas Gleixner
2016-07-07 8:47 ` [tip:timers/core] timers: Optimize collect_expired_timers() " tip-bot for Anna-Maria Gleixner
2016-07-04 9:50 ` [patch 4 18/22] tick/sched: Remove pointless empty function Thomas Gleixner
2016-07-07 8:47 ` [tip:timers/core] timers/nohz: Remove pointless tick_nohz_kick_tick() function tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 19/22] timer: Forward wheel clock whenever possible Thomas Gleixner
2016-07-07 8:48 ` [tip:timers/core] timers: Forward the " tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 20/22] timer: Only wake softirq if necessary Thomas Gleixner
2016-07-07 8:48 ` [tip:timers/core] timers: " tip-bot for Thomas Gleixner
2016-07-04 9:50 ` [patch 4 21/22] timer: Split out index calculation Thomas Gleixner
2016-07-07 8:48 ` [tip:timers/core] timers: " tip-bot for Anna-Maria Gleixner
2016-07-04 9:50 ` [patch 4 22/22] timer: Optimization for same expiry time in mod_timer() Thomas Gleixner
2016-07-07 8:49 ` [tip:timers/core] timers: Implement optimization " tip-bot for Anna-Maria Gleixner
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