linux-kernel - Re: [git-pull -tip] x86: cpu

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Message-Id: <1241007294.3061.12.camel@ht.satnam>
Date:	Wed, 29 Apr 2009 17:44:54 +0530
From:	Jaswinder Singh Rajput <jaswinder@...nel.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [git-pull -tip] x86: cpu_debug patches

On Wed, 2009-04-29 at 12:50 +0200, Ingo Molnar wrote:
> * Jaswinder Singh Rajput <jaswinder@...nel.org> wrote:
> 
> > On Tue, 2009-04-28 at 19:28 +0200, Ingo Molnar wrote:
> > > * Jaswinder Singh Rajput <jaswinder@...nel.org> wrote:
> > > 
> > > > @@ -850,10 +903,10 @@ static int cpu_init_cpu(void)
> > > >  		cpui = &cpu_data(cpu);
> > > >  		if (!cpu_has(cpui, X86_FEATURE_MSR))
> > > >  			continue;
> > > > -		per_cpu(cpu_model, cpu) = ((cpui->x86_vendor << 16) |
> > > > -					   (cpui->x86 << 8) |
> > > > -					   (cpui->x86_model));
> > > > -		per_cpu(cpu_modelflag, cpu) = get_cpu_modelflag(cpu);
> > > > +		per_cpu(cpu_modelflag, cpu) = get_cpu_flag(cpui);
> > > > +		if (!per_cpu(cpu_modelflag, cpu))
> > > > +			send_report(per_cpu(cpu_priv_count, cpu), cpui);
> > > 
> > > This means that if the CPU is not enumerated in the model table 
> > > explicitly, we'll fall back to some really minimal output, right?
> > > 
> > 
> > Yes.
> 
> That's a bug really: it means that for every new CPU type that comes 
> around we need to update this code. I.e. precisely for those CPUs 
> where we might need the most help from such a debug facility, we 
> wont have much info to look at ... New CPUs generally support all 
> the CPU features that are displayed here, in a compatible manner.
> 
> So that needs to be improved/changed to not be tied to such a static 
> 'cpu model' enumeration but instead be CPU feature flags driven. See 
> all the existing cpu_has_*() tests we have.
> 

cpu_has_*() is based on boot_cpu. So you mean cpu_has tests. right ?

We can use cpu_has tests for unknown processors but 'cpu model' is
accurate and cover all range.

cpu_has does not cover following registers:
1. platform
2. poweron
3. control
4. bios
5. freq
6. cache
7. misc
8. base
9. ver
10. conf

So is this looks OK to you:

1. first check for 'cpu model' if CPU not supported then goto 2
2. check for cpu_has tests 

--
JSR




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