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

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Date:	Tue, 14 Jun 2016 18:48:57 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	George Spelvin <linux@...encehorizons.net>
cc:	peterz@...radead.org, edumazet@...gle.com,
	linux-kernel@...r.kernel.org, richardcochran@...il.com
Subject: Re: [patch 13/20] timer: Switch to a non cascading wheel

On Tue, 14 Jun 2016, George Spelvin wrote:
> Not enough to be interesting, and the extra levels increase processing
> time.  If you need to shrink TIMER_ARRAYMASK to fit another flag bit,
> the easier way would be to encode only the level rather than the index,
> since you can derive the latter from level and expiry time trivially.
 
We can accomodate wheel with 512 buckets with the current ARRAYMASK and that
really should be enough.
 
> A couple of really minor tweaks that could be folded in, if Thomas feels
> like it:
> 
> * It would make sense to move all the TIMER_ARRAYSHIFT/TIMER_ARRAYMASK
>   stuff out of patch 13 and into patch 20.

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

> * It would make sense to change the return type of mod_timer (& Co.)
>   detach_if_pending, and del_timer to bool.
>   ({try_to_,}del_timer_sync return 3 values.)

We can do that as a seperate patch. Makes sense. 

Thanks,

	tglx