linux-kernel - Re: [PATCH v6 1/5] powerpc/85xx: implement hardware timebase sync

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Message-Id: <D2BA086B-6EB3-4853-B901-FA37DCCDC134@kernel.crashing.org>
Date:	Thu, 28 Jun 2012 13:30:26 -0500
From:	Kumar Gala <galak@...nel.crashing.org>
To:	Zhao Chenhui <chenhui.zhao@...escale.com>
Cc:	"linuxppc-dev@...ts.ozlabs.org list" <linuxppc-dev@...ts.ozlabs.org>,
	Scott Wood <scottwood@...escale.com>,
	"linux-kernel@...r.kernel.org list" <linux-kernel@...r.kernel.org>,
	Li Yang <leoli@...escale.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH v6 1/5] powerpc/85xx: implement hardware timebase sync


On Jun 28, 2012, at 5:50 AM, Benjamin Herrenschmidt wrote:

> On Thu, 2012-06-28 at 11:38 +0800, Zhao Chenhui wrote:
>> 
>> 
>> The bootloader have done a timebase sync. If we do not need KEXEC or
>> HOTPLUG_CPU feature, it is unnecessary to do it again at boot time of
>> kernel. I only compile the timebase sync routines
>> when users enable KEXEC or HOTPLUG_CPU. 
> 
> Still, how much are you really saving ? Is it worth the added mess and
> loss of test coverage ?
> 
> We have too many conditional stuff like that already.
> 
> Cheers,
> Ben.
> 

I'd also be interested to know how long it actually takes to do time base sync this way.  Since you are freezing the timers for some period how long does it really take between the freeze/unfreeze in mpc85xx_give_timebase()

+	mpc85xx_timebase_freeze(1);
...
+	mpc85xx_timebase_freeze(0);

You can use ATBL/U as a way to see # of cycles taken.

- k--
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