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

From: Thomas Gleixner <tglx@linutronix.de>
To: George Spelvin <linux@sciencehorizons.net>
Cc: peterz@infradead.org, edumazet@google.com,
	linux-kernel@vger.kernel.org, richardcochran@gmail.com
Subject: Re: [patch 13/20] timer: Switch to a non cascading wheel
Date: Tue, 14 Jun 2016 18:48:57 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.11.1606141840490.5839@nanos> (raw)
In-Reply-To: <20160614125800.18461.qmail@ns.sciencehorizons.net>

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