Messages in this thread | | | Date | Mon, 12 Mar 2007 17:24:05 +0100 | From | "Joerg Roedel" <> | Subject | Re: [PATCH 4/4 TRY#3] optimize and simplify get_cycles_sync() |
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On Mon, Mar 12, 2007 at 06:08:11PM +0200, Avi Kivity wrote: > Joerg Roedel wrote: > >On Fri, Mar 09, 2007 at 08:10:03PM +0200, Avi Kivity wrote: > > > >>Joerg Roedel 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. > >>> > >>> +#define RDTSCP ".byte 0x0f, 0x01, 0xf9" > >>>+ alternative_io_two("cpuid\nrdtsc", > >>>+ "rdtsc", X86_FEATURE_SYNC_RDTSC, > >>>+ ".byte 0x0f, 0x01, 0xf9", X86_FEATURE_RDTSCP, > >>> > >>why not use the RDTSCP macro here? > >> > > > >Does this macro exist? I couldn't found it in the current git tree. And > >the rdtscp macros in msr.h use the plain opcode too. > > > > -ENOCOFFEE? You defined the macro 3 lines above the .byte directive...
Yes, lack of coffee, and even worse -EBLINDHACKER :-(
-- Joerg Roedel Operating System Research Center AMD Saxony LLC & Co. KG
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