>
> On Mon, Mar 27, 2017 at 08:47:37AM -0700, kan.li...@intel.com wrote:
> > From: Kan Liang <kan.li...@intel.com>
> >
> > Having msr_set/clear_bit on many cpus or given CPU can avoid extra
> > unnecessory IPIs
>
> How does that happen?
>
My previous patch did a read-modify-write operation. Compared with the
single operation set/clear, it will has extra IPIs.
Sorry for the confusing wording.
I will change the description.
> You have smp_call_function_many() sending IPIs to each CPU in the mask.
> Doesn't look like avoiding anything to me.
>
> Now if you want to have interfaces set/clear_bit_on_cpu(s), that's a
> different story.
>
> And those actually double the amount of IPIs the moment you do a read-
> modify-write operation on the MSR, i.e., you want to read *and* write
> afterwards.
>
> If you only want to do a single operation - set or clear - like you're doing
> in
> your other patch, then I guess that's fine as it wraps the
> smp_call_function* boilerplate code.
>
> > and simplify MSR content manipulation, when it only needs to flip a
> > bit.
> > There is already msr_set/clear_bit, but missing the _on_cpu and
> > _on_cpus version.
> >
> > Signed-off-by: Kan Liang <kan.li...@intel.com>
> > ---
> > arch/x86/include/asm/msr.h | 29 ++++++++++++++++++
> > arch/x86/lib/msr-smp.c | 76
> ++++++++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 105 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
> > index 898dba2..9bc999b 100644
> > --- a/arch/x86/include/asm/msr.h
> > +++ b/arch/x86/include/asm/msr.h
> > @@ -20,6 +20,11 @@ struct msr {
> > };
> > };
> >
> > +struct msr_bit_info {
> > + u32 msr_no;
> > + u8 bit;
> > +};
>
> No, not *another* struct msr*info. Please reuse msr_info.
>
OK.
Thanks,
Kan
