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From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: fweisbec@redhat.com, Paolo Bonzini <pbonzini@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>, X86 ML <x86@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Mike Galbraith <umgwanakikbuti@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Rik van Riel <riel@redhat.com>,
	williams@redhat.com, "Paul E. McKenney" <paulmck@us.ibm.com>
Subject: Re: [PATCH 3/3] context_tracking,x86: remove extraneous irq disable & enable from context tracking on syscall entry
Date: Thu, 7 May 2015 14:49:39 +0200	[thread overview]
Message-ID: <20150507124938.GA17675@gmail.com> (raw)
In-Reply-To: <20150507124437.GB17443@gmail.com>


* Ingo Molnar <mingo@kernel.org> wrote:

> The TIF_RCU_QS thing is just a fancy way for synchronize_rcu() 
> (being executed on some other CPU not doing RT work) to 
> intelligently wait for the remote (RT work doing) CPU to finish 
> executing kernel code, without polling or so.

it's basically a cheap IPI being inserted on the remote CPU.

We need the TIF_RCU_QS callback not just to wait intelligently, but 
mainly to elapse a grace period, otherwise synchronize_rcu() might not 
ever make progress: think a SCHED_FIFO task doing some kernel work, 
synchronize_rcu() stumbling upon it - but the SCHED_FIFO task 
otherwise never scheduling and never getting any timer irqs either, 
and thus never entering quiescent state.

(Cc:-ed Paul too, he might be interested in this as well.)

Thanks,

	Ingo

  reply	other threads:[~2015-05-07 12:49 UTC|newest]

Thread overview: 83+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-04-30 21:23 [PATCH 0/3] reduce nohz_full syscall overhead by 10% riel
2015-04-30 21:23 ` [PATCH 1/3] reduce indentation in __acct_update_integrals riel
2015-04-30 21:23 ` [PATCH 2/3] remove local_irq_save from __acct_update_integrals riel
2015-04-30 21:23 ` [PATCH 3/3] context_tracking,x86: remove extraneous irq disable & enable from context tracking on syscall entry riel
2015-04-30 21:56   ` Andy Lutomirski
2015-05-01  6:40   ` Ingo Molnar
2015-05-01 15:20     ` Rik van Riel
2015-05-01 15:59       ` Ingo Molnar
2015-05-01 16:03         ` Andy Lutomirski
2015-05-01 16:21           ` Ingo Molnar
2015-05-01 16:26             ` Rik van Riel
2015-05-01 16:34               ` Ingo Molnar
2015-05-01 18:05                 ` Rik van Riel
2015-05-01 18:40                   ` Ingo Molnar
2015-05-01 19:11                     ` Rik van Riel
2015-05-01 19:37                       ` Andy Lutomirski
2015-05-02  5:27                         ` Ingo Molnar
2015-05-02 18:27                           ` Rik van Riel
2015-05-03 18:41                           ` Andy Lutomirski
2015-05-07 10:35                             ` Ingo Molnar
2015-05-04  9:26                           ` Paolo Bonzini
2015-05-04 13:30                             ` Rik van Riel
2015-05-04 14:06                             ` Rik van Riel
2015-05-04 14:19                             ` Rik van Riel
2015-05-04 15:59                             ` question about RCU dynticks_nesting Rik van Riel
2015-05-04 18:39                               ` Paul E. McKenney
2015-05-04 19:39                                 ` Rik van Riel
2015-05-04 20:02                                   ` Paul E. McKenney
2015-05-04 20:13                                     ` Rik van Riel
2015-05-04 20:38                                       ` Paul E. McKenney
2015-05-04 20:53                                         ` Rik van Riel
2015-05-05  5:54                                           ` Paul E. McKenney
2015-05-06  1:49                                             ` Mike Galbraith
2015-05-06  3:44                                               ` Mike Galbraith
2015-05-06  6:06                                                 ` Paul E. McKenney
2015-05-06  6:52                                                   ` Mike Galbraith
2015-05-06  7:01                                                     ` Mike Galbraith
2015-05-07  0:59                                           ` Frederic Weisbecker
2015-05-07 15:44                                             ` Rik van Riel
2015-05-04 19:00                               ` Rik van Riel
2015-05-04 19:39                                 ` Paul E. McKenney
2015-05-04 19:59                                   ` Rik van Riel
2015-05-04 20:40                                     ` Paul E. McKenney
2015-05-05 10:53                                   ` Peter Zijlstra
2015-05-05 12:34                                     ` Paul E. McKenney
2015-05-05 13:00                                       ` Peter Zijlstra
2015-05-05 18:35                                         ` Paul E. McKenney
2015-05-05 21:09                                           ` Rik van Riel
2015-05-06  5:41                                             ` Paul E. McKenney
2015-05-05 10:48                                 ` Peter Zijlstra
2015-05-05 10:51                                   ` Peter Zijlstra
2015-05-05 12:30                                     ` Paul E. McKenney
2015-05-02  4:06                   ` [PATCH 3/3] context_tracking,x86: remove extraneous irq disable & enable from context tracking on syscall entry Mike Galbraith
2015-05-01 16:37             ` Ingo Molnar
2015-05-01 16:40               ` Rik van Riel
2015-05-01 16:45                 ` Ingo Molnar
2015-05-01 16:54                   ` Rik van Riel
2015-05-01 17:12                     ` Ingo Molnar
2015-05-01 17:22                       ` Rik van Riel
2015-05-01 17:59                         ` Ingo Molnar
2015-05-01 16:22           ` Rik van Riel
2015-05-01 16:27             ` Ingo Molnar
2015-05-03 13:23       ` Mike Galbraith
2015-05-03 17:30         ` Rik van Riel
2015-05-03 18:24           ` Andy Lutomirski
2015-05-03 18:52             ` Rik van Riel
2015-05-07 10:48               ` Ingo Molnar
2015-05-07 12:18                 ` Frederic Weisbecker
2015-05-07 12:29                   ` Ingo Molnar
2015-05-07 15:47                     ` Rik van Riel
2015-05-08  7:58                       ` Ingo Molnar
2015-05-07 12:22                 ` Andy Lutomirski
2015-05-07 12:44                   ` Ingo Molnar
2015-05-07 12:49                     ` Ingo Molnar [this message]
2015-05-08  6:17                       ` Paul E. McKenney
2015-05-07 12:52                     ` Andy Lutomirski
2015-05-07 15:08                       ` Ingo Molnar
2015-05-07 17:47                         ` Andy Lutomirski
2015-05-08  6:37                           ` Ingo Molnar
2015-05-08 10:59                             ` Andy Lutomirski
2015-05-08 11:27                               ` Ingo Molnar
2015-05-08 12:56                                 ` Andy Lutomirski
2015-05-08 13:27                                   ` Ingo Molnar

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