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Date: Mon, 12 Mar 2007 14:02:45 +0100 From: "Joerg Roedel" <joerg.roedel@....com> To: "Avi Kivity" <avi@...o.co.il> cc: discuss@...-64.org, "Andi Kleen" <ak@...e.de>, linux-kernel@...r.kernel.org Subject: Re: [PATCH 4/4 TRY#3] optimize and simplify get_cycles_sync() On Fri, Mar 09, 2007 at 08:10:03PM +0200, Avi Kivity wrote: > Joerg Roedel wrote: > >From: Joerg Roedel <joerg.roedel@....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. Regards, Joerg -- Joerg Roedel Operating System Research Center AMD Saxony LLC & Co. KG - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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