Messages in this thread | | | Subject | Re: [PATCH 3/3] x86, cpu: Change NOP selection for certain Intel CPUs | From | Steven Rostedt <> | Date | Mon, 18 Apr 2011 19:34:34 -0400 |
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On Mon, 2011-04-18 at 15:36 -0700, H. Peter Anvin wrote: > Due to a decoder implementation quirk, some specific Intel CPUs > actually perform better with the "k8_nops" than with the > SDM-recommended NOPs. For runtime-selected NOPs, if we detect those > specific CPUs then use the k8_nops instead of the ones we would > normally use. > > Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> > Cc: Tejun Heo <tj@kernel.org> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Frederic Weisbecker <fweisbec@gmail.com> > Cc: Jason Baron <jbaron@redhat.com> > --- > arch/x86/kernel/alternative.c | 9 ++++++++- > 1 files changed, 8 insertions(+), 1 deletions(-) > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index 2ca3f65..34bf87e 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -190,7 +190,14 @@ void __init arch_init_ideal_nops(void) > { > switch (boot_cpu_data.x86_vendor) { > case X86_VENDOR_INTEL:
Please add:
/* * Due to a decoder implementation quirk, some specific Intel CPUs * actually perform better with the "k8_nops" than with the * SDM-recommended NOPs. For runtime-selected NOPs, if we detect those * specific CPUs then use the k8_nops instead of the ones we would * normally use. */
I tend to read comments by the code more than change logs that added the code.
Thanks,
-- Steve
> - if (boot_cpu_has(X86_FEATURE_NOPL)) { > + if (boot_cpu_data.x86 == 6 && > + boot_cpu_data.x86_model >= 0x0f && > + boot_cpu_data.x86_model != 0x1c && > + boot_cpu_data.x86_model != 0x26 && > + boot_cpu_data.x86_model != 0x27 && > + boot_cpu_data.x86_model < 0x30) { > + ideal_nops = k8_nops; > + } else if (boot_cpu_has(X86_FEATURE_NOPL)) { > ideal_nops = p6_nops; > } else { > #ifdef CONFIG_X86_64
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