Re: [RFC PATCH 7/8] x86/lib_user_wait.h: Add APIs for user wait instructions

[Fenghua Yu]

On Wed, Jun 20, 2018 at 12:34:32AM +0200, Thomas Gleixner wrote:
> On Tue, 19 Jun 2018, Fenghua Yu wrote:
> > On Tue, Jun 19, 2018 at 11:12:05AM +0200, Thomas Gleixner wrote:
> > > On Fri, 15 Jun 2018, Fenghua Yu wrote:
> > > 
> > > > A few new user wait instructions UMONITOR, UMWAIT, and TPAUSE are
> > > > published in the latest Intel Instruction Set Extensions document.
> > > > 
> > > > Define the APIs for user or kernel to use the instructions.
> > > 
> > > You're not defining APIs. You're adding a pile of misdesigned helper
> > > functions which again add static storage per compilation unit and CPUID
> > > fiddling.
> > > 
> > > If you want to add proper APIs then add the stuff to the VDSO and be done
> > > with it.
> > 
> > The user wait instructions are mainly called by user apps; but they can
> > be used in kernel as well.
> > 
> > I'm planning to provide five APIs to user:
> > 1. If user wait feature is supported
> > 2. nsec to tsc translation
> > 3. umonitor function that exectes UMONITOR instruction
> > 4. umwait function that executes UMWAIT instruction
> > 5. tpause function that executes TPAUSE instruction
> > 
> > Seems 1-2 can be implemented in VDSO. But should I implement 3-5 in
> > VDSO/kernel as well?
> 
> If you want a real API, then yes. If not, then an UAPI header is definitely
> not the place for this.

Sure. I will implement the APIs in VDSO.

Thanks.

-Fenghua