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Subject: Re: [PATCH v6 1/5] powerpc/85xx: implement hardware timebase sync
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From: Kumar Gala <galak@kernel.crashing.org>
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Date: Thu, 28 Jun 2012 13:30:26 -0500
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To: Zhao Chenhui <chenhui.zhao@freescale.com>
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On Jun 28, 2012, at 5:50 AM, Benjamin Herrenschmidt wrote:

> On Thu, 2012-06-28 at 11:38 +0800, Zhao Chenhui wrote:
>>=20
>>=20
>> 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.=20
>=20
> Still, how much are you really saving ? Is it worth the added mess and
> loss of test coverage ?
>=20
> We have too many conditional stuff like that already.
>=20
> Cheers,
> Ben.
>=20

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=