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From: Chris Metcalf <cmetcalf@mellanox.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Gilad Ben Yossef <giladb@mellanox.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Rik van Riel <riel@redhat.com>, Tejun Heo <tj@kernel.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"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>,
	Michal Hocko <mhocko@suse.com>, <linux-mm@kvack.org>,
	<linux-doc@vger.kernel.org>, <linux-api@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v15 04/13] task_isolation: add initial support
Date: Mon, 29 Aug 2016 12:53:30 -0400	[thread overview]
Message-ID: <ccd4a21a-8de5-38f0-5e78-1ad999755b7a@mellanox.com> (raw)
In-Reply-To: <20160829164809.GW10153@twins.programming.kicks-ass.net>

On 8/29/2016 12:48 PM, Peter Zijlstra wrote:
> On Mon, Aug 29, 2016 at 12:40:32PM -0400, Chris Metcalf wrote:
>> On 8/29/2016 12:33 PM, Peter Zijlstra wrote:
>>> On Tue, Aug 16, 2016 at 05:19:27PM -0400, Chris Metcalf wrote:
>>>> +	/*
>>>> +	 * Request rescheduling unless we are in full dynticks mode.
>>>> +	 * We would eventually get pre-empted without this, and if
>>>> +	 * there's another task waiting, it would run; but by
>>>> +	 * explicitly requesting the reschedule, we may reduce the
>>>> +	 * latency.  We could directly call schedule() here as well,
>>>> +	 * but since our caller is the standard place where schedule()
>>>> +	 * is called, we defer to the caller.
>>>> +	 *
>>>> +	 * A more substantive approach here would be to use a struct
>>>> +	 * completion here explicitly, and complete it when we shut
>>>> +	 * down dynticks, but since we presumably have nothing better
>>>> +	 * to do on this core anyway, just spinning seems plausible.
>>>> +	 */
>>>> +	if (!tick_nohz_tick_stopped())
>>>> +		set_tsk_need_resched(current);
>>> This is broken.. and it would be really good if you don't actually need
>>> to do this.
>> Can you elaborate?
> Naked use of TIF_NEED_RESCHED like this is busted. There is more state
> that needs to be poked to keep things consistent / working.

Would it be cleaner to just replace the set_tsk_need_resched() call
with something like:

     set_current_state(TASK_INTERRUPTIBLE);
     schedule();
     __set_current_state(TASK_RUNNING);

or what would you recommend?

Or, as I said, just doing a busy loop here while testing to see
if need_resched or signal had been set?

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com

  reply	other threads:[~2016-08-29 18:28 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 [this message]
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
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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