linux-kernel - Re: [PATCH] cpufreq: pass policy to ->get() driver callback

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Date:	Thu, 10 Sep 2015 23:40:16 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
	Kristen Carlson Accardi <kristen@...ux.intel.com>,
	open list <linux-kernel@...r.kernel.org>,
	Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH] cpufreq: pass policy to ->get() driver callback

On Thursday, September 10, 2015 06:52:22 AM Viresh Kumar wrote:
> On 10-09-15, 03:41, Rafael J. Wysocki wrote:

[cut]

> > Passing a pointer and dereferencing it is generally less efficient than passing
> > a number.  Before the patch the core has to do the dereference before calling
> > ->get, so it likely doesn't matter here, but the code churn from this change
> > is quite substantial and the benefit from it is in the noise IMO.
> 
> Hmm.. Actually almost every other callback (bios_limit() is another
> one), passes the policy to the driver, and I thought always passing
> the policy will make it more symmetrical. And the expectation that the
> cpufreq drivers wouldn't need to use policy from the ->get() callback
> would be wrong. Even if there are only few users today. One is the
> acpi-cpufreq driver and others are the ones, that are using
> cpufreq_generic_get() :)

So the whole question is whether or not this is worth the whole code churn
related to the exchange of callbacks.

At this point I really don't know.  It depends on the design discussion I'd
like to start.

Thanks,
Rafael

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