linux-kernel - Re: [PATCH] ring-buffer: More precise time stamps for nested writes

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Message-ID: <20150327221430.GA31309@iris.ozlabs.ibm.com>
Date:	Sat, 28 Mar 2015 09:14:30 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"Suresh E. Warrier" <warrier@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] ring-buffer: More precise time stamps for nested writes

On Fri, Mar 27, 2015 at 12:04:15PM -0400, Steven Rostedt wrote:
> On Fri, 27 Mar 2015 00:38:43 -0500
> "Suresh E. Warrier" <warrier@...ux.vnet.ibm.com> wrote:
> 
> > > But for now, what can be done is to have
> > > a flag that is set that will implement this or not. Using
> > > static_branch() to implement it such that when its off it has no effect.
> > > 
> > 
> > Are you recommending that for now I use a static_branch() instead
> > of a CONFIG option to fix this? I could do that but the resulting 
> > code will either be messier to read (with several if condition checks)
> > or will require some duplication of code. My assumption is that the
> > new CONFIG option when disabled should have negligible impact since
> > the compiler inlines the functions.
> 
> It can be done cleanly if you encapsulate it properly.

Sure, but what is the advantage to using a static branch?  When would
you ever want a single kernel image that could run either way
depending on what machine it was running on?

> Too bad I'm not going on any trips soon. This is a project I would work
> on on the plane.

:)

Paul.

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