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

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Date:	Thu, 23 Feb 2012 08:50:27 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Venkatesh Pallipadi <venki@...gle.com>
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

* 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.

> +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.

Thanks,

	Ingo
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