linux-kernel - Re: [patch 13/20] timer: Switch to a non cascading wheel

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Message-ID: <20160614195653.16933.qmail@ns.sciencehorizons.net>
Date:	14 Jun 2016 15:56:53 -0400
From:	"George Spelvin" <linux@...encehorizons.net>
To:	linux@...encehorizons.net, tglx@...utronix.de
Cc:	edumazet@...gle.com, linux-kernel@...r.kernel.org,
	peterz@...radead.org, richardcochran@...il.com
Subject: Re: [patch 13/20] timer: Switch to a non cascading wheel

Thomas Gleixner wrote:
> On Tue, 14 Jun 2016, George Spelvin wrote:
>> If you need to shrink TIMER_ARRAYMASK to fit another flag bit,
> 
> We can accomodate wheel with 512 buckets with the current ARRAYMASK and that
> really should be enough.

You're absolutely correct, but I was referring to the possible development
in the future of the need for another flag bit for some purpose *other*
than encoding a bucket number.  There's no need now, but if next year
someone finds and urgent need for another flag bit, there's a way
to proceed.

(Although you could just enlarge "flags"; the removal of "slack" has left
a 32-bit alignment hole.)

> The expiry code uses the pending_map already in patch 13 to avoid looking at
> the bucket if its empty.

My bad, I'm sorry!  I was quickly re-reading it and missed that.
Given the quality of the patch series, I should have expected that and
looked harder.

> Thanks,

Thank *you*.  It really is a pleasure to read.  I can't find anything but the most
insignificant issues to complain about.