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

Andrew Morton
2007-03-07T00:25:54Z

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?