linux-kernel - Re: [RFC][PATCH] tracing: Remove useless 4 bytes of padding from every event

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Message-ID: <20120516201431.GA29661@redhat.com>
Date:	Wed, 16 May 2012 16:14:31 -0400
From:	Dave Jones <davej@...hat.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	David Sharp <dhsharp@...gle.com>,
	Vaibhav Nagarnaik <vnagarnaik@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH] tracing: Remove useless 4 bytes of padding from
 every event

On Wed, May 16, 2012 at 01:07:14PM -0700, Arjan van de Ven wrote:
 > On 5/16/2012 1:04 PM, Linus Torvalds wrote:
 > > On Wed, May 16, 2012 at 1:00 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
 > >>
 > >> Seriously though. What's your take on changing the kernel that will
 > >> break an older distro. Obviously, this change is too early to apply. But
 > >> because an old distro has one app that will break if we make a change in
 > >> the kernel, is that enough to keep that change out?
 > > 
 > > I suspect that powertop is enough of a developer thing that if that's
 > > the only thing that breaks, we don't have to worry too much.
 > > 
 > > I don't want to break *everybody*, so new distro's should be
 > > up-to-date. But breaking something like a F14-15 timeframe distro or
 > > something staid like a SLES (or "Debian Stale" or whatever they call
 > > that thing that only takes crazy-old binaries)? It's fine. We don't
 > > want to *rush* into it, but no, if those distros are basically not
 > > updating, we can't care about them forever for something like
 > > powertop.
 > 
 > agreed.
 > 
 > I would say something like "6 months" (e.g. 3.6); anybody who's likely
 > to update anything will have done the powertop upgrade from his distro
 > by then, and anybody who isn't isn't going to update the kernel either.

One possibility would be a config symbol to enable the deprecated field
(kind of like what we did with compat vdso).  Distros that have a new
enough powertop can then disable it.

	Dave

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