Date: Mon, 5 Sep 2005 10:04:24 -0700
From: Nishanth Aravamudan <nacc@us.ibm.com>
To: Srivatsa Vaddagiri <vatsa@in.ibm.com>, Con Kolivas <kernel@kolivas.org>,
       linux-kernel@vger.kernel.org, akpm@osdl.org,
       ck list <ck@vds.kolivas.org>
Subject: Re: [PATCH 1/3] dynticks - implement no idle hz for x86
Message-ID: <20050905170424.GK25856@us.ibm.com>
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> <20050905070053.GA7329@in.ibm.com> <20050905084425.B24051@flint.arm.linux.org.uk>
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On 05.09.2005 [08:44:25 +0100], Russell King wrote:
> On Mon, Sep 05, 2005 at 12:30:53PM +0530, Srivatsa Vaddagiri wrote:
> > On Sun, Sep 04, 2005 at 01:10:54PM -0700, Nishanth Aravamudan wrote:
> > > First of all, and maybe this is just me, I think it would be good to
> > > make the dyn_tick_timer per-interrupt source, as opposed to each arch?
> > 
> > Nish, may be a good idea as it may make the code more cleaner (it will
> > remove the 'if (cpu_has_local_apic())' kind of code that is there
> > currently in x86). However note that ARM currently has 'handler' member also 
> > part of it, which is used to recover time and that has nothing to do with 
> > interrupt source. Unless there is something like John's TOD, we still
> > need to recover time in a arch-dependent fashion ..Where do you
> > propose to have that 'handler' member?
> 
> Exactly where it is.  It's there because of the problem you allude to
> above - it's there to catch up system time.  Any generic code can't
> answer the question "how much time has passed since we disabled the
> timer" without additional information.

I agree.

> However, we could change "handler" to be a function pointer which
> returns the number of missed ticks instead, and then updates the
> kernels time and tick keeping.  That would probably be more efficient.

Yes, I think

unsigned long (*recover_time)(int, void *, struct pt_regs *);

or something similar (not sure about the params), might be more
appropriate.

Thanks,
Nish

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