linux-kernel - Re: [PATCH] [4/7] Convert TSC disabling to generic cpuid disable bitmap

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Date:	Sat, 19 Jan 2008 22:29:13 +0000
From:	Ian Campbell <ijc@...lion.org.uk>
To:	Andi Kleen <ak@...e.de>
Cc:	mingo@...e.hu, hpa@...or.com, tglx@...utronix.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [4/7] Convert TSC disabling to generic cpuid disable
	bitmap


On Sat, 2008-01-19 at 19:57 +0100, Andi Kleen wrote:
> On Saturday 19 January 2008 19:15:48 Ian Campbell wrote:
> > diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> > index 6f5c74a..b3721fd 100644
> > --- a/arch/x86/xen/time.c
> > +++ b/arch/x86/xen/time.c
> > @@ -592,7 +592,7 @@ __init void xen_time_init(void)
> >  	set_normalized_timespec(&wall_to_monotonic,
> >  				-xtime.tv_sec, -xtime.tv_nsec);
> >  
> > -	setup_clear_cpu_cap(X86_FEATURE_TSC);
> > +	setup_force_cpu_cap(X86_FEATURE_TSC);
> 
> Actually that would be only needed if someone else disabled TSC explicitely before.
> 
> Simply deleting this should be sufficient. Does this patch work for you?

Yes.

> It would break if someone passes notsc to a Xen kernel, but then a lot of options make the kernel
> break if you don't know what you're doing so that doesn't seem like a big issue.

I'm happy either way. I think the Xen paravirt subsystem will use TSC
where it has to due to the Xen architecture regardless of this setting.

Ian.
-- 
Ian Campbell

Good day for overcoming obstacles.  Try a steeplechase.

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