linux-kernel - Re: [RFC] Timer: Migrate running timers

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Date:	Wed, 20 Nov 2013 19:57:29 +0530
From:	viresh kumar <viresh.kumar@...aro.org>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	bigeasy@...utronix.de, rostedt@...dmis.org, tj@...nel.org,
	mingo@...hat.com, peterz@...radead.org,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	john.stultz@...aro.org, paulmck@...ux.vnet.ibm.com
Subject: Re: [RFC] Timer: Migrate running timers

On Wednesday 20 November 2013 05:12 PM, Thomas Gleixner wrote:
> Viresh,
> 
> On Wed, 20 Nov 2013, Viresh Kumar wrote:
> 
>> Migration of timers from idle cores to non-idle ones for power saving is very
>> well working and really saves a lot of power for us. What's currently not
>> working is the migration of running timers Or timers which re-arms themselves.
>>
>> There are complications with migrating timers which schedules themselves again
>> from their handler. del_timer_sync() can't detect that the timer's handler
>> yet has not finished.
> 
> Because you try to violate the semantics of the existing code. There
> is a reason why we enforce that running timers must be requeued on the
> base they are running on.
> 
> Now you try to duct tape it into submission. That's not going to fly.
> 
> The timer wheel code is not designed to allow that and it has lots of
> other short comings and historic burdens. I'm not going to accept more
> duct tape and fragile hackery into that code.
> 
> I'm already working on a complete replacement infrastructure, which
> avoids all the short comings of the current timer implementation
> including this one. 
> 
> It's going to be a massive effort to convert everything over to the
> new infrastructure so we can kill the timer wheel, but that's less
> scary and less risky than trying to add more fragility to the existing
> code.

Thanks for the feedback. I Atleast know now that this patch doesn't have a future :)

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