Re: [Xen-devel] [PATCH] x86: Adjust rdtsc inline assembly

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 18/02/15 13:11, Jan Beulich wrote:
>>>> On 18.02.15 at 13:25, <andrew.cooper3@xxxxxxxxxx> wrote:
>> The single use of the old rdtsc() in emulate_privileged_op() is altered to 
>> use
>> the new rdtsc() and the rdmsr_writeback path to set eax/edx appropriately.
> I'm not entirely sure about this one - the current code surely is slightly
> faster than the replacement. Question is how much this matters. I'd
> suggest to be on the safe side and simply open-code the asm() there.

It is a matter of a 4 instructions on a fault slowpath, which which only
ever executed in the unlikely case that vtsc is enabled on a domain, or
the kernel has set CR4.TSD.

I would not loose sleep over the introduced inefficiently.

~Andrew


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