linux-kernel - Re: [PATCH] Extend mwait idle to optimize away CAL and RES interrupts to an idle CPU -v1

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Message-ID: <CABeCy1YnuD_O_aj_unpRGsokPtSpcRLRKRA-PF07rg8Rk-z_cg@mail.gmail.com>
Date:	Thu, 23 Feb 2012 12:03:48 -0800
From:	Venki Pallipadi <venki@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Aaron Durbin <adurbin@...gle.com>,
	Paul Turner <pjt@...gle.com>,
	Yong Zhang <yong.zhang0@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Extend mwait idle to optimize away CAL and RES interrupts
 to an idle CPU -v1

[ Resending without the ugly email client formatting ]

On Wed, Feb 22, 2012 at 11:50 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Venkatesh Pallipadi <venki@...gle.com> wrote:
>
>> * Do we need some accounting for these wakeups exported for powertop?
>
> If then tracepoints.
>
>> * We can also eliminate TS_POLLING flag in favor of this. But, that will have
>>   a lot more touchpoints and better done as a standlone change.
>
> Should most definitely be done for this series to be acceptble -
> as a preparatory patch in the series, with the feature at the
> end of the series.
>
OK. Will look at TS_POLLING part and likely include it in the next resend.

>> +DECLARE_PER_CPU(atomic_t *, idle_task_ti_flags);
>
> That's ugly, we should access the idle task's ti flags directly.
>
> To have efficient percpu access to the idle threads another
> clean-up is needed: we should turn idle_thread_array into a
> full-structure PER_CPU area.
>
> For that we need a small variant of fork_idle(), which does not
> dup the init thread - pretty trivial.
>
> fork_idle() should also make sure it does not schedule the child
> thread: thus we'd also be able to further simplify smpboot.c and
> get rid of all that extremely ugly 'struct create_idle'
> gymnastics in smpboot.c.
>

Hmm. Not being very familiar with that code, I will have to take a closer
look at this potential cleanup...

Thanks,
Venki

> Thanks,
>
>        Ingo
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