Re: [PATCH] softtsc (was RE: [Xen-devel] Guest TSC and Xen (Intel and AMD feedback please))

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 9/7/08 22:32, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

> The attached patch adds a new Xen boot option "softtsc" that
> causes all hvm domains to trap and emulate all rdtsc instructions
> and fetch Xen system time instead of the hardware tsc.  As
> a result, the processor will appear to be running at 1000.xyz MHz
> (where xyz indicates some fraction that seems to vary slightly
> across different boots).  I've also added a line of output to
> "xm debug-key t" to report softsc and tsc-related CPU features.
> 
> (Keir, though 3.3 functionality freeze is past, this is more of a
> diagnostic aid and defaults off, so I don't know if you would
> consider it for 3.3.)

Yes, I will take it, but have the following comments.
 1. Why do you define new boolean 'constant_tsc'? Can you just use
test_bit(X86_FEATURE_CONSTANT_TSC)?
 2. Your change in common/keyhandler.c breaks ia64. :-)
 3. Your change to arch/x86/time.c looks unnecessary.
 4. Should you catch SVM's RDTSCP vmexit as well as RDTSC?

 -- Keir




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