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From: "George Spelvin" <linux@sciencehorizons.net>
To: linux@sciencehorizons.net, tglx@linutronix.de
Cc: edumazet@google.com, linux-kernel@vger.kernel.org,
	peterz@infradead.org, richardcochran@gmail.com
Subject: Re: [patch 13/20] timer: Switch to a non cascading wheel
Date: 14 Jun 2016 06:15:06 -0400	[thread overview]
Message-ID: <20160614101506.30068.qmail@ns.sciencehorizons.net> (raw)
In-Reply-To: <alpine.DEB.2.11.1606141045191.5839@nanos>

On Tue, 14 Jun 2016, Thomas Gleixner wrote:
> I thought about that and when looking at those long timeout thingies
> I came to the conclusion that it's simply not worth the trouble.

Okay.  A comment might be nice, just to stop someone else wasting
brain power on it.  E.g.

/*
 * If the timer happens to expire exactly now, this will cascade it to
 * vectors[0] which we just cleared and won't check again for 64 jiffies.
 * This is acceptable error on a timeout this long.
 */

>> to be replaced with __builtin_clz or similar:
> 
> Except that __fls() is noticeably slower than the if chain.

Fair enogh.  I wasn't sure about the distribution; if it's biased low,
then the if chain would win.

> That's not new code. We kept the ordering, but yes, we definitely can turn
> that around. The only restriction is that we get it before releasing the lock.

Thanks!

  reply	other threads:[~2016-06-14 10:15 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-14  8:16 [patch 13/20] timer: Switch to a non cascading wheel George Spelvin
2016-06-14  8:50 ` Thomas Gleixner
2016-06-14 10:15   ` George Spelvin [this message]
2016-06-14 10:20 ` Peter Zijlstra
2016-06-14 12:58   ` George Spelvin
2016-06-14 16:48     ` Thomas Gleixner
2016-06-14 19:56       ` George Spelvin
  -- strict thread matches above, loose matches on Subject: below --
2016-06-13  8:40 [patch 00/20] timer: Refactor the timer wheel Thomas Gleixner
2016-06-13  8:41 ` [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner
2016-06-13 11:40   ` Peter Zijlstra
2016-06-13 12:30     ` Thomas Gleixner
2016-06-13 12:46       ` Eric Dumazet
2016-06-13 14:30         ` Thomas Gleixner
2016-06-14 10:11       ` Ingo Molnar
2016-06-14 16:28         ` Thomas Gleixner
2016-06-14 17:14           ` Arjan van de Ven
2016-06-14 18:05             ` Thomas Gleixner
2016-06-14 20:34               ` Peter Zijlstra
2016-06-14 20:42               ` Peter Zijlstra
2016-06-14 21:17                 ` Eric Dumazet
2016-06-15 14:53                   ` Thomas Gleixner
2016-06-15 14:55                     ` Arjan van de Ven
2016-06-15 16:43                       ` Thomas Gleixner
2016-06-16 15:43                         ` Thomas Gleixner
2016-06-16 16:02                           ` Paul E. McKenney
2016-06-16 18:14                             ` Peter Zijlstra
2016-06-17  0:40                               ` Paul E. McKenney
2016-06-17  4:04                                 ` Paul E. McKenney
2016-06-16 16:04                           ` Arjan van de Ven
2016-06-16 16:09                             ` Thomas Gleixner
2016-06-15 15:05                     ` Eric Dumazet
2016-06-13 14:36   ` Richard Cochran
2016-06-13 14:39     ` Thomas Gleixner

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