linux-kernel - Re: [gcv v3 06/35] scheduler: Replace __get_cpu

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Message-ID: <20130830065418.GA13867@gmail.com>
Date:	Fri, 30 Aug 2013 08:54:18 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Tejun Heo <tj@...nel.org>, akpm@...uxfoundation.org,
	Ingo Molnar <mingo@...hat.com>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [gcv v3 06/35] scheduler: Replace __get_cpu_var uses


* Christoph Lameter <cl@...ux.com> wrote:

> On Thu, 29 Aug 2013, Steven Rostedt wrote:
> 
> > On Thu, Aug 29, 2013 at 04:57:43PM +0000, Christoph Lameter wrote:
> > >
> > > We could add a ____this_cpu variant that would be used in the cases we do
> > > not want preemption checks? There should not be too many but it will
> > > mean a whole lot of new definitions in percpu.h.
> >
> > Let's get away from underscores as they are meaningless.
> >
> > A this_cpu_atomic() or other descriptive name would be much more
> > appropriate.
> 
> Its not really an atomic operation in the classic sense.
> 
> this_cpu_no_preempt_check_read ?
> 
> The problem that I have is also that a kernel with preemption is not 
> something that see anywhere these days. Looks more like an academic 
> exercise? Does this really matter? All the distro I see use 
> PREEMPT_VOLUNTARY. Performance degradation is significant if massive 
> amounts of checks and preempt disable/enable points are added to the 
> kernel.
> 
> Do we agree that it is necessary and useful to add another variant of 
> this_cpu ops for this? The concern of having too many variants is no 
> longer there? Adding another variant is not that difficult just code 
> intensive.

Just stop the lame excuses and fix it already. This has come up in the 
past and you know it: you were told to fix the this_cpu debug checks by 
Linus as well, yet you didn't ... Don't send crap you know is broken.

Thanks,

	Ingo
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