Re: [PATCH 4/4] optimize and simplify get_cycles_sync()

Joerg Roedel
2007-03-09T09:59:58Z

On Tue, Mar 06, 2007 at 04:25:41PM -0800, Andrew Morton wrote:
> On Wed, 28 Feb 2007 15:25:54 +0100
> "Joerg Roedel" <joerg.roedel@amd.com> wrote:
>
> > From: Joerg Roedel <joerg.roedel@amd.com>
> >
> > This patch simplifies the get_cycles_sync() function by removing the
> > #ifdefs from it. Further it introduces an optimization for AMD
> > processors. There the RDTSCP instruction is used instead of CPUID;RDTSC
> > which is helpfull if the kernel runs as a KVM guest. Running as a guest
> > makes CPUID very expensive because it causes an intercept of the guest.
>
> Problem:
>
> http://test.kernel.org/functional/index.html
>
> lots of builds fell over because their binutils versions don't understand
> rdtscp.
>
> I don't know how recently rdtscp support was added to binutils, but
> this is likely to be a problem. Perhaps we can change this patch to
> embed the hex code for that opcode instead?

Ok, I will submit an updated version soon. Thanks for pointing this out.

Joerg