From: Thomas Gleixner <tglx@linutronix.de>
To: George Spelvin <linux@horizon.com>
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
viresh.kumar@linaro.org
Subject: Re: [patch 2/7] timer: Remove FIFO guarantee
Date: Tue, 9 Jun 2015 10:05:56 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.11.1506091001020.4133@nanos> (raw)
In-Reply-To: <20150609053930.25020.qmail@ns.horizon.com>
On Tue, 9 Jun 2015, George Spelvin wrote:
> Thomas Gleixner wrote:
>
> > After thinking more about it, I'm even more sure that any code which
> > relies on the FIFO "guarantee" is broken today.
>
> Indeed, I am completely convinced. All I might request is a reassignment
> of blame in the commit message.
Will do. Thanks for spotting it!
> Thank you for your comments on my other blue-sky ideas, too.
>
> I need to look into why we're using wheels, and what the point is.
> How much of an advantage do they have over an efficient priority queue
> like a pairing heap?
The only reason is performance. The wheel has O(1) insertion and
deletion time while heaps and trees usually have O(log(n)).
Timer wheel timers are usually timeouts and 99% of them are canceled
before expiry. Networking is probably the heaviest use case followed
by disk I/O.
Thanks,
tglx
next prev parent reply other threads:[~2015-06-09 8:06 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-05 22:27 [patch 2/7] timer: Remove FIFO guarantee George Spelvin
2015-06-08 17:48 ` Thomas Gleixner
2015-06-09 5:39 ` George Spelvin
2015-06-09 8:05 ` Thomas Gleixner [this message]
2015-06-09 9:43 ` George Spelvin
2015-06-09 10:24 ` Peter Zijlstra
2015-06-09 11:15 ` George Spelvin
-- strict thread matches above, loose matches on Subject: below --
2015-05-26 22:50 [patch 0/7] timers: Footprint diet and NOHZ overhead mitigation Thomas Gleixner
2015-05-26 22:50 ` [patch 2/7] timer: Remove FIFO guarantee Thomas Gleixner
2015-05-27 9:11 ` Viresh Kumar
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