From: "George Spelvin" <linux@horizon.com>
To: linux@horizon.com, tglx@linutronix.de
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
viresh.kumar@linaro.org
Subject: Re: [patch 2/7] timer: Remove FIFO guarantee
Date: 9 Jun 2015 01:39:30 -0400 [thread overview]
Message-ID: <20150609053930.25020.qmail@ns.horizon.com> (raw)
In-Reply-To: <alpine.DEB.2.11.1506081930550.4133@nanos>
Thomas Gleixner wrote:
> It does. Depending on when you enqueue the timer because the thing is
> calculated from the delta (expires - jiffies).
Ah, right. If slack > 0, the slack amount is absolute and the rounding
will be consistent.
But if slack < 0, which is the default, it's a percentage of remaining
jiffies. Since slack only delays timeouts, an earlier-scheduled
timeout could easily be delayed more.
(There are only six calls to set_timer_slack() to change the default
to something positive in the kernel.)
>> I'm not disagreeing with the change, but it's not clear to me that
>> it's as safe as you think.
> 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.
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?
next prev parent reply other threads:[~2015-06-09 5:39 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 [this message]
2015-06-09 8:05 ` Thomas Gleixner
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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