linux-kernel - Re: [PATCH] cpuidle: powernv/pseries: Decrease the snooze residency

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Message-ID: <20150530060141.GA19134@dirshya.in.ibm.com>
Date:	Sat, 30 May 2015 11:31:41 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org,
	Daniel Lezcano <daniel.lezcano@...aro.org>, rjw@...ysocki.net,
	linux-kernel@...r.kernel.org, anton@...ba.org,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH] cpuidle: powernv/pseries: Decrease the snooze residency

* Preeti U Murthy <preeti@...ux.vnet.ibm.com> [2015-05-29 19:17:17]:

[snip]

> > +	if (max_idle_state > 1) {
> > +		snooze_timeout_en = true;
> > +		snooze_timeout = cpuidle_state_table[1].target_residency *
> > +				 tb_ticks_per_usec;
> > +	}
> 
> Any idea why we don't have snooze defined on the shared lpar configuration ?

In shared lpar case, spinning in guest context may potentially take
away cycles from other lpars waiting to run on the same physical cpu.

So the policy in shared lpar case is to let PowerVM hypervisor know
immediately that the guest cpu is idle which will allow the hypervisor
to use the cycles for other tasks/lpars.

--Vaidy

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