linux-kernel - Re: [PATCH] intel_idle: use static_key to optimize idle enter/exit paths

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Message-ID: <CAJvTdKkZoo1yO0N4ra8SBh0XY4PiY+KWkVysGptfhVWYb8kO1g@mail.gmail.com>
Date:	Mon, 28 Jul 2014 16:38:40 -0400
From:	Len Brown <lenb@...nel.org>
To:	Jason Baron <jbaron@...mai.com>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] intel_idle: use static_key to optimize idle enter/exit paths

On Fri, Jul 11, 2014 at 1:54 PM, Jason Baron <jbaron@...mai.com> wrote:
> If 'arat' is set in the cpuflags, we can avoid the checks for entering/exiting
> the tick broadcast code entirely. It would seem that this is a hot enough code
> path to make this worthwhile. I ran a few hackbench runs, and consistenly see
> reduced branches and cycles.

Hi Jason,

Your logic looks right -- though I've never used this
static_key_slow_inc() stuff.
I'm impressed that something in user-space could detect this change.

Can you share how to run the workload where you detected a difference,
and describe the hardware you measured?

thanks,
-Len Brown, Intel Open Source Technology Center
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