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Date: Tue, 4 Apr 2017 09:43:43 +0530
From: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: Anton Blanchard <anton@ozlabs.org>, benh@kernel.crashing.org,
 paulus@samba.org, mpe@ellerman.id.au, ego@linux.vnet.ibm.com,
 rjw@rjwysocki.net, daniel.lezcano@linaro.org,
 linuxppc-dev@lists.ozlabs.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH 1/3] cpuidle: powernv: Don't bounce between low and very
 low thread priority
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* Nicholas Piggin <npiggin@gmail.com> [2017-04-04 09:52:07]:

> On Tue,  4 Apr 2017 07:54:12 +1000
> Anton Blanchard <anton@ozlabs.org> wrote:
> 
> > From: Anton Blanchard <anton@samba.org>
> > 
> > The core of snooze_loop() continually bounces between low and very
> > low thread priority. Changing thread priorities is an expensive
> > operation that can negatively impact other threads on a core.
> > 
> > All CPUs that can run PowerNV support very low priority, so we can
> > avoid the change completely.
> 
> This looks good. I have HMT_lowest() which does alt feature patching
> we can use for pseries and default idle code.

Alternatively, if we are going to set priority only once in various
other places, HMT_low(); HMT_very_low(); should not add to extra
cycles.  Let me code that up.

--Vaidy