linux-kernel - Re: [PATCH] tick-broadcast: Register for hrtimer based broadcast as the default broadcast mode

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Date:	Mon, 08 Dec 2014 10:59:31 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Mark Rutland <mark.rutland@....com>
CC:	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jingchang.lu@...escale.com" <jingchang.lu@...escale.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] tick-broadcast: Register for hrtimer based broadcast
 as the default broadcast mode

On 12/05/2014 07:09 PM, Mark Rutland wrote:
> Hi Preeti,
> 
> Moving this out of the architecture code looks good to me!
> 
> I have a couple of minor comments below.
<snip>

>>  
>> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
>> index ec1791f..6044a51 100644
>> --- a/kernel/time/timekeeping.c
>> +++ b/kernel/time/timekeeping.c
>> @@ -1016,6 +1016,10 @@ void __init timekeeping_init(void)
>>  		boot.tv_sec = 0;
>>  		boot.tv_nsec = 0;
>>  	}
>> +	/* Register for hrtimer based broadcast as the default timekeeping
>> +	 * mode in deep idle states.
>> +	 */
> 
> Nit: for code style this should have a newline after the '/*' (and we
> should probably have a newline before that anyway.
> 
>> +	tick_setup_hrtimer_broadcast();
> 
> We register the generic dummy timer via an early_initcall, which keeps
> all the logic in the dummy timer driver. Are we able to do the same of
> the broadcast hrtimer? Or is there some ordering constraint we need to
> meet?

Yes this is doable. There are no ordering constraints. Placing it in an
early_initcall() will enable it to run before initializing SMP and
cpuidle, which is perfect (we do not have any per-cpu initializations
and we do not want cpus to begin entering idle states before this
hrtimer is initialized).

It also runs after the hrtimer/clockevents infrastructure has been
initialized, which is good since we need them. The broadcast hrtimer
will thus only get registered as a broadcast device if no other clock
device has managed to register itself as one.

Let me send out a V2.

Thanks

Regards
Preeti U Murthy

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