linux-kernel - Re: [PATCH 1/2] i386: mce cleanup part1: functional change

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Message-ID: <1152.1191962806@turing-police.cc.vt.edu>
Date:	Tue, 09 Oct 2007 16:46:46 -0400
From:	Valdis.Kletnieks@...edu
To:	Oleg Verych <olecom@...wer.upol.cz>
Cc:	Joerg Roedel <joerg.roedel@....com>,
	Andi Kleen <andi@...stfloor.org>,
	Christoph Egger <Christoph.Egger@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] i386: mce cleanup part1: functional change

On Tue, 09 Oct 2007 18:32:30 +0200, Oleg Verych said:
> On Tue, Oct 09, 2007 at 06:06:05PM +0200, Joerg Roedel wrote:
> > > cpu_has() returns int,
> > > but would it be better to have something like
> > > 
> > >   	if (!mce_disabled &&
> > > 	    !(c->x86_capability & (X86_FEATURE_MCA | X86_FEATURE_MCE)) {
> > > 		printk(KERN_INFO "CPU%i: No machine check support available\n",
> > > 			smp_processor_id());
> > 
> > This looks complicated and is harder to read. Its exactly the purpose of the
> > cpu_has() macro to avoid such constructs.
> 
> It is done via test_bit(), which is designed for IO access with all that
> `const volatile' stuff, 2 x unnecessary, can't be optimized here (IMHO).

If this code is getting called often enough that optimization matters, you
got *bigger* issues to worry about than optimization.  Looks like it should
only happen once at boot time.

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