linux-kernel - Re: [RFC] sched: Add a new lockless wake-from-idle implementation

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Date:	Thu, 13 Feb 2014 10:38:00 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <bitbucket@...ine.de>, X86 ML <x86@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] sched: Add a new lockless wake-from-idle implementation


* Andy Lutomirski <luto@...capital.net> wrote:

> This is a strawman proposal to simplify the idle implementation, eliminate
> a race
> 
> Benefits over current code:
>  - ttwu_queue_remote doesn't use an IPI unless needed

Cool.

>  - The diffstat should speak for itself :)

Neat!

>  - Less racy.  Spurious IPIs are possible, but only in narrow windows or
>    when two wakeups occur in rapid succession.
>  - Seems to work (?)
> 
> Issues:
>  - Am I doing the percpu stuff right?
>  - Needs work on non-x86 architectures

Absolutely, and with the least amount of disruption possible, as 
people are not very good at testing 'all' of them.

>  - The !CONFIG_SMP case needs to be checked

Which also happens to be the default for half of all non-x86 arches.

>  - Is "idlepoll" a good name for the new code?  It doesn't have *that*
>    much to do with the idle state.  Maybe cpukick?

'cpukick', hands down.

> If this turns out okay, TIF_NEED_RESCHED could possibly be deleted as well.

Cool ...

Thanks,

	Ingo
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