Re: [PATCH 5/5] x86/intel_rdt: hotcpu updates for RDT

[Shivappa Vikas]

On Wed, 1 Mar 2017, Thomas Gleixner wrote:

> >  	WARN_ON(c->x86_cache_occ_scale != cqm_l3_scale);
> >
> > @@ -1585,12 +1580,17 @@ static int intel_cqm_cpu_starting(unsigned int cpu)
> >
> >  static int intel_cqm_cpu_exit(unsigned int cpu)
> >  {
> > +	struct intel_pqr_state *state = &per_cpu(pqr_state, cpu);
>
> Can be this_cpu_ptr() because the callback is guaranteed to run on the
> outgoing CPU.

Will fix this. Assumed the calls are setup cache alloc way - 
cpuhp_setup_state(CPUHP_AP_ONLINE_DYN ..

> >  	int target;
> >
> >  	/* Is @cpu the current cqm reader for this package ? */
> >  	if (!cpumask_test_and_clear_cpu(cpu, &cqm_cpumask))
> >  		return 0;
>
> So if the CPU is not the current cqm reader then the per cpu state of this
> CPU is left stale. Great improvement.
>
> > +	state->rmid = 0;
> > +	state->rmid_usecnt = 0;
> > +	wrmsr(MSR_IA32_PQR_ASSOC, 0, state->closid);
>
> What clears state->closid? And what guarantees that state->rmid is not
> updated before the CPU has really gone away?

- The rdt code takes care of clearing closid state now. Will update the comment. 
- The cqm however was never writing a zero to PQR_ASSOC.

So the update needs to be - to remove the state->closid = 0 from cqm code as the 
rdt code takes care of closid state in clear_closid() called from both offline and 
online cpu.
And also write a rmid = 0 to PQR_ASSOC.

We can integrate the two of these hot cpu calls(from cat and cqm) to write PQR 
only once.

guess I can skip all of these and send it as part of cqm changes we planned 
anyways, because this is really a cqm change.

Thanks,
Vikas