linux-kernel - RE: [PATCH v4 6/7] x86/vdso: Introduce CPU number helper functions

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Date:   Fri, 22 Jun 2018 18:46:28 +0000
From:   "Bae, Chang Seok" <chang.seok.bae@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     Andy Lutomirski <luto@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Ingo Molnar" <mingo@...nel.org>, Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Metzger, Markus T" <markus.t.metzger@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v4 6/7] x86/vdso: Introduce CPU number helper functions

On Friday, 22 Jun 2018, Thomas Gleixner wrote: 
> On Wed, 20 Jun 2018, Chang S. Bae wrote:
> > CPU number initialization in vDSO is now a bit cleaned up by
> > the new helper functions. The helper functions will take
> > care of combing CPU and node number and reading each from

> s/combing/combining/ please

Will fix.

> > @@ -18,9 +18,9 @@ __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *unused)
> >       p = __getcpu();

> While we are touching this, can we please as a first step change __getcpu()
> to something else? I've tripped over this several times in the past and
> confused it with a (nonexisting) variant of get_cpu().

How about __vdso_get_cpudata()?

> >  #ifdef CONFIG_NUMA
> >       node = cpu_to_node(cpu);
> >  #endif

> While at it please get rid of the ifdeffery. If CONFIG_NUMA=n then
> cpu_to_node(cpu) resolves to (0).

Okay, will fix this.


> >
> >       if (cpu)
> > -             *cpu = p & VGETCPU_CPU_MASK;
> > +             *cpu = lsl_tscp_to_cpu(p);
> >
> >       if (node)
> > -             *node = p >> 12;
> > +             *node = lsl_tscp_to_node(p);
>
> Are these new helpers going to be used at some other place than this? If
> not, then there is really no point at all. Then just go and make this:
>
> __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *unused)
> {
>         vdso_read_cpu_and_node(cpu, node);
>         return 0;
> }

> > @@ -340,19 +340,19 @@ static void vgetcpu_cpu_init(void *arg)
> >       int cpu = smp_processor_id();
> >       struct desc_struct d = { };
> >       unsigned long node = 0;
> > +     unsigned long cpu_number = 0;
>
> That's hardly a CPU number. It's encoded CPU and node information.
>
> > +     cpu_number = make_lsl_tscp(cpu, node);
>
> So the whole thing can be reduced to:
>
>         u64 cpudata = vdso_encode_cpu_and_node(cpu, cpu_to_node(cpu));
>
> Or some other sensible function name.

Now, for these helper function renaming, I would like to check it from Andy.

Thanks, 
Chang