linux-kernel - Re: [RFC PATCH v3 0/5] powerpc: Support context tracking for Power pSeries

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Message-ID: <20130529213159.GD17419@somewhere>
Date:	Wed, 29 May 2013 23:32:01 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Li Zhong <zhong@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, paulmck@...ux.vnet.ibm.com,
	paulus@...ba.org, michael@...erman.id.au,
	Anton Blanchard <anton@....ibm.com>
Subject: Re: [RFC PATCH v3 0/5] powerpc: Support context tracking for Power
 pSeries

On Mon, May 13, 2013 at 06:59:23PM +1000, Benjamin Herrenschmidt wrote:
> On Mon, 2013-05-13 at 16:03 +0800, Li Zhong wrote:
> > 
> > To my understanding, it is used to enable RCU user extended quiescent
> > state, so RCU on that cpu doesn't need scheduler ticks. And together
> > with some other code(already in 3.10), we are able to remove the ticks
> > in some cases (e.g. only 1 task running on the cpu, with some other
> > limitations).
> 
> Ok, sounds interesting. Once you fix the little cosmetic issue, I don't
> see any reason not to merge them as it's basically wiring up an existing
> feature (in that regard the patches are pretty straightforward) and I
> assume the overhead is only there when you enable it.

Yeah when CONFIG_RCU_USER_QS=n and CONFIG_VIRT_CPU_ACCOUNTING_GEN=n this
should be zero overhead. And those configs are only needed for full dynticks.

Thanks.

> 
> Cheers,
> Ben.
> 
> 
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