linux-kernel - Re: [PATCH x86] [12/16] Optimize lock prefix switching to run less frequently

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Date:	Fri, 4 Jan 2008 13:17:30 +0100
From:	Andi Kleen <ak@...e.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH x86] [12/16] Optimize lock prefix switching to run less frequently

On Friday 04 January 2008 10:42:17 Thomas Gleixner wrote:
> On Thu, 3 Jan 2008, Andi Kleen wrote:
> > This makes a significant difference in boot up performance on AMD SimNow!
> > Also I expect it to be a little faster on native systems too because a smp 
> > switch does a lot of text_poke()s which each synchronize the pipeline.
> 
> Please run your patches through checkpatch.pl.
> 
> ERROR: use tabs not spaces
> #48: FILE: arch/x86/kernel/alternative.c:360:


I saw a lot of these warnings, but disregarded them as obviously silly. I don't
have plans to redo all the patches for that.
  
> > +
> > +		/* Only switch to UP mode if we don't immediately boot others */
> > +		if (num_possible_cpus() == 1 || max_cpus == 0)
> 
> Shouldn't this be max_cpus <= 1 ?

Don't think so, smp_init() seems to use it one off.
 
> > +extern unsigned int max_cpus;
> 
> I'm a bit wary about making max_cpus global. max_cpus is used all over
> the place as a local variable name. Can we please rename it to
> setup_max_cpus or something like that?

Hmm, I didn't see any warnings from this so surely it's not a big issue?

-Andi
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