From: Luiz Capitulino <lcapitulino@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>,
Gilad Ben Yossef <giladb@mellanox.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Rik van Riel <riel@redhat.com>, Tejun Heo <tj@kernel.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Christoph Lameter <cl@linux.com>,
Viresh Kumar <viresh.kumar@linaro.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Andy Lutomirski <luto@amacapital.net>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Francis Giraldeau <francis.giraldeau@gmail.com>,
Andi Kleen <andi@firstfloor.org>, Arnd Bergmann <arnd@arndb.de>,
linux-kernel@vger.kernel.org
Subject: Re: task isolation discussion at Linux Plumbers
Date: Fri, 11 Nov 2016 15:54:56 -0500 [thread overview]
Message-ID: <20161111155456.0b8b8589@redhat.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1611071753040.3709@nanos>
On Mon, 7 Nov 2016 17:55:47 +0100 (CET)
Thomas Gleixner <tglx@linutronix.de> wrote:
> On Sat, 5 Nov 2016, Chris Metcalf wrote:
> > == Remote statistics ==
> >
> > We discussed the possibility of remote statistics gathering, i.e. load
> > average etc. The idea would be that we could have housekeeping
> > core(s) periodically iterate over the nohz cores to load their rq
> > remotely and do update_current etc. Presumably it should be possible
> > for a single housekeeping core to handle doing this for all the
> > nohz_full cores, as we only need to do it quite infrequently.
> >
> > Thomas suggested that this might be the last remaining thing that
> > needed to be done to allow disabling the current behavior of falling
> > back to a 1 Hz clock in nohz_full.
> >
> > I believe Thomas said he had a patch to do this already.
>
> No, Riek was working on that.
Rik series made it possible to have remote tick sampling. That is,
calling account_process_tick(cpu) from a housekeeping CPU, so that
tick accounting is done for a remote "cpu". The series was intended
to improve overhead on nohz_full CPUs.
However, to get rid of the 1Hz tick, we need to do the same thing
for scheduler_tick(). I'm not sure if this has been attempted yet,
and if it's at all possible.
> > == Remote LRU cache drain ==
> >
> > One of the issues with task isolation currently is that the LRU cache
> > drain must be done prior to entering userspace, but it requires
> > interrupts enabled and thus can't be done atomically. My previous
> > patch series have handled this by checking with interrupts disabled,
> > but then looping around with interrupts enabled to try to drain the
> > LRU pagevecs. Experimentally this works, but it's not provable that
> > it terminates, which is worrisome. Andy suggested adding a percpu
> > flag to disable creation of deferred work like LRU cache pages.
> >
> > Thomas suggested using an RT "local lock" to guard the LRU cache
> > flush; he is planning on bringing the concept to mainline in any case.
> > However, after some discussion we converged on simply using a spinlock
> > to guard the appropriate resources. As a result, the
> > lru_add_drain_all() code that currently queues work on each remote cpu
> > to drain it, can instead simply acquire the lock and drain it remotely.
> > This means that a task isolation task no longer needs to worry about
> > being interrupted by SMP function call IPIs, so we don't have to deal
> > with this in the task isolation framework any more.
> >
> > I don't recall anyone else volunteering to tackle this, so I will plan
> > to look at it. The patch to do that should be orthogonal to the
> > revised task isolation patch series.
>
> I offered to clean up the patch from RT. I'll do that in the next days.
Yes, the RT kernel got a patch that fixes this. I wonder if the same
idea could work for vm_stat (that is, gathering those stats from
housekeeping CPUs vs. having to queue deferrable work to do it).
next prev parent reply other threads:[~2016-11-11 20:55 UTC|newest]
Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-16 21:19 [PATCH v15 00/13] support "task_isolation" mode Chris Metcalf
2016-08-16 21:19 ` [PATCH v15 01/13] vmstat: add quiet_vmstat_sync function Chris Metcalf
2016-08-16 21:19 ` [PATCH v15 02/13] vmstat: add vmstat_idle function Chris Metcalf
2016-08-16 21:19 ` [PATCH v15 03/13] lru_add_drain_all: factor out lru_add_drain_needed Chris Metcalf
2016-08-16 21:19 ` [PATCH v15 04/13] task_isolation: add initial support Chris Metcalf
2016-08-29 16:33 ` Peter Zijlstra
2016-08-29 16:40 ` Chris Metcalf
2016-08-29 16:48 ` Peter Zijlstra
2016-08-29 16:53 ` Chris Metcalf
2016-08-30 7:59 ` Peter Zijlstra
2016-08-30 7:58 ` Peter Zijlstra
2016-08-30 15:32 ` Chris Metcalf
2016-08-30 16:30 ` Andy Lutomirski
2016-08-30 17:02 ` Chris Metcalf
2016-08-30 18:43 ` Andy Lutomirski
2016-08-30 19:37 ` Chris Metcalf
2016-08-30 19:50 ` Andy Lutomirski
2016-09-02 14:04 ` Chris Metcalf
2016-09-02 17:28 ` Andy Lutomirski
2016-09-09 17:40 ` Chris Metcalf
2016-09-12 17:41 ` Andy Lutomirski
2016-09-12 19:25 ` Chris Metcalf
2016-09-27 14:22 ` Frederic Weisbecker
2016-09-27 14:39 ` Peter Zijlstra
2016-09-27 14:51 ` Frederic Weisbecker
2016-09-27 14:48 ` Paul E. McKenney
2016-09-30 16:59 ` Chris Metcalf
2016-09-01 10:06 ` Peter Zijlstra
2016-09-02 14:03 ` Chris Metcalf
2016-09-02 16:40 ` Peter Zijlstra
2017-02-02 16:13 ` Eugene Syromiatnikov
2017-02-02 18:12 ` Chris Metcalf
2016-08-16 21:19 ` [PATCH v15 05/13] task_isolation: track asynchronous interrupts Chris Metcalf
2016-08-16 21:19 ` [PATCH v15 06/13] arch/x86: enable task isolation functionality Chris Metcalf
2016-08-30 21:46 ` Andy Lutomirski
2016-08-16 21:19 ` [PATCH v15 07/13] arm64: factor work_pending state machine to C Chris Metcalf
2016-08-17 8:05 ` Will Deacon
2016-08-16 21:19 ` [PATCH v15 08/13] arch/arm64: enable task isolation functionality Chris Metcalf
2016-08-26 16:25 ` Catalin Marinas
2016-08-16 21:19 ` [PATCH v15 09/13] arch/tile: " Chris Metcalf
2016-08-16 21:19 ` [PATCH v15 10/13] arm, tile: turn off timer tick for oneshot_stopped state Chris Metcalf
2016-08-16 21:19 ` [PATCH v15 11/13] task_isolation: support CONFIG_TASK_ISOLATION_ALL Chris Metcalf
2016-08-16 21:19 ` [PATCH v15 12/13] task_isolation: add user-settable notification signal Chris Metcalf
2016-08-16 21:19 ` [PATCH v15 13/13] task_isolation self test Chris Metcalf
2016-08-17 19:37 ` [PATCH] Fix /proc/stat freezes (was [PATCH v15] "task_isolation" mode) Christoph Lameter
2016-08-20 1:42 ` Chris Metcalf
2016-09-28 13:16 ` Frederic Weisbecker
2016-08-29 16:27 ` Ping: [PATCH v15 00/13] support "task_isolation" mode Chris Metcalf
2016-09-07 21:11 ` Francis Giraldeau
2016-09-07 21:39 ` Francis Giraldeau
2016-09-08 16:21 ` Francis Giraldeau
2016-09-12 16:01 ` Chris Metcalf
2016-09-12 16:14 ` Peter Zijlstra
2016-09-12 21:15 ` Rafael J. Wysocki
2016-09-13 0:05 ` Rafael J. Wysocki
2016-09-13 16:00 ` Francis Giraldeau
2016-09-13 0:20 ` Francis Giraldeau
2016-09-13 16:12 ` Chris Metcalf
2016-09-27 14:49 ` Frederic Weisbecker
2016-09-27 14:35 ` Frederic Weisbecker
2016-09-30 17:07 ` Chris Metcalf
2016-11-05 4:04 ` task isolation discussion at Linux Plumbers Chris Metcalf
2016-11-05 16:05 ` Christoph Lameter
2016-11-07 16:55 ` Thomas Gleixner
2016-11-07 18:36 ` Thomas Gleixner
2016-11-07 19:12 ` Rik van Riel
2016-11-07 19:16 ` Will Deacon
2016-11-07 19:18 ` Rik van Riel
2016-11-11 20:54 ` Luiz Capitulino [this message]
2016-11-09 1:40 ` Paul E. McKenney
2016-11-09 11:14 ` Andy Lutomirski
2016-11-09 17:38 ` Paul E. McKenney
2016-11-09 18:57 ` Will Deacon
2016-11-09 19:11 ` Paul E. McKenney
2016-11-10 1:44 ` Andy Lutomirski
2016-11-10 4:52 ` Paul E. McKenney
2016-11-10 5:10 ` Paul E. McKenney
2016-11-11 17:00 ` Andy Lutomirski
2016-11-09 11:07 ` Frederic Weisbecker
2016-12-19 14:37 ` Paul E. McKenney
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