Message-ID: <431F11FF.2000704@tmr.com>
Date: Wed, 07 Sep 2005 12:14:55 -0400
From: Bill Davidsen <davidsen@tmr.com>
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To: vatsa@in.ibm.com
CC: Con Kolivas <kernel@kolivas.org>, linux-kernel@vger.kernel.org,
       akpm@osdl.org, ck list <ck@vds.kolivas.org>, rmk+lkml@arm.linux.org.uk
Subject: Re: [PATCH 1/3] dynticks - implement no idle hz for x86
References: <20050831165843.GA4974@in.ibm.com> <200509031801.09069.kernel@kolivas.org> <20050903090650.B26998@flint.arm.linux.org.uk> <200509031814.49666.kernel@kolivas.org> <20050904201054.GA4495@us.ibm.com> <20050904212616.B11265@flint.arm.linux.org.uk> <20050905053225.GA4294@in.ibm.com> <20050905054813.GC25856@us.ibm.com> <20050905063229.GB4294@in.ibm.com>
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Srivatsa Vaddagiri wrote:
> On Sun, Sep 04, 2005 at 10:48:13PM -0700, Nishanth Aravamudan wrote:
> 
>>Admittedly, I don't think SMP ARM has been around all that long? Maybe
>>the existing code just has not been extended.
> 
> 
> Yeah, maybe ARM never cared for SMP. But we do care :)
> 
> 
>>I'm not sure on this. It's going to be NULL for other architectures, or
>>end up being called by the reprogram() call for the last CPU to go idle,
>>right (presuming there isn't a separate TOD source, like in x86). I
>>think it is better to be in the reprogram() interface.
> 
> 
> Non-x86 could have it set to NULL, in which case it doesn't get called.
> (I know the current code does not take care of this situation).
> But having an explicit 'all_cpus_idle' interface may be good, since 
> Tony talked of idling some devices when all CPUs are idle. So it
> probably has non-x86/PIT uses too.

If this is intended to reduce power, and it originally came from that 
root, then this is the time to put in a hook for transitions to<=>from 
the all-idle state. Various arch may have things other than the PIT 
which should (or at least can) be stopped, and which need to be restarted.

-- 
    -bill davidsen (davidsen@tmr.com)
"The secret to procrastination is to put things off until the
  last possible moment - but no longer"  -me
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