Re: [PATCH 17/21] x86/intel_rdt/cqm: Add sched_in support

[Shivappa Vikas]

On Sun, 2 Jul 2017, Thomas Gleixner wrote:

> On Mon, 26 Jun 2017, Vikas Shivappa wrote:
> >  DECLARE_PER_CPU(struct intel_pqr_state, pqr_state);
> >  DECLARE_PER_CPU_READ_MOSTLY(int, cpu_closid);
> > +DECLARE_PER_CPU_READ_MOSTLY(int, cpu_rmid);
> >  DECLARE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
> > +DECLARE_STATIC_KEY_FALSE(rdt_mon_enable_key);
> > +DECLARE_STATIC_KEY_FALSE(rdt_enable_key);
>
> Please make this a two stage change. Add rdt_enable_key first and then the
> monitoring stuff. Ideally you introduce rdt_enable_key here and in the
> control code in one go.
>
> > +static void __intel_rdt_sched_in(void)
> >  {
> > -	if (static_branch_likely(&rdt_alloc_enable_key)) {
> > -		struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
> > -		int closid;
> > +	struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
> > +	u32 closid = 0;
> > +	u32 rmid = 0;
> >
> > +	if (static_branch_likely(&rdt_alloc_enable_key)) {
> >  		/*
> >  		 * If this task has a closid assigned, use it.
> >  		 * Else use the closid assigned to this cpu.
> > @@ -55,14 +59,31 @@ static inline void intel_rdt_sched_in(void)
> >  		closid = current->closid;
> >  		if (closid == 0)
> >  			closid = this_cpu_read(cpu_closid);
> > +	}
> > +
> > +	if (static_branch_likely(&rdt_mon_enable_key)) {
> > +		/*
> > +		 * If this task has a rmid assigned, use it.
> > +		 * Else use the rmid assigned to this cpu.
> > +		 */
> > +		rmid = current->rmid;
> > +		if (rmid == 0)
> > +			rmid = this_cpu_read(cpu_rmid);
> > +	}
> >
> > -		if (closid != state->closid) {
> > -			state->closid = closid;
> > -			wrmsr(IA32_PQR_ASSOC, state->rmid, closid);
> > -		}
> > +	if (closid != state->closid || rmid != state->rmid) {
> > +		state->closid = closid;
> > +		state->rmid = rmid;
> > +		wrmsr(IA32_PQR_ASSOC, rmid, closid);
>
> This can be written smarter.
>
> 	struct intel_pqr_state newstate = this_cpu_read(rdt_cpu_default);
> 	struct intel_pqr_state *curstate = this_cpu_ptr(&pqr_state);
>
> 	if (static_branch_likely(&rdt_alloc_enable_key)) {
> 		if (current->closid)
> 			newstate.closid = current->closid;
> 	}
>
> 	if (static_branch_likely(&rdt_mon_enable_key)) {
> 		if (current->rmid)
> 			newstate.rmid = current->rmid;
> 	}
>
> 	if (newstate != *curstate) {
> 		*curstate = newstate;
> 		wrmsr(IA32_PQR_ASSOC, newstate.rmid, newstate.closid);
> 	}
>
> The unconditional read of rdt_cpu_default is the right thing to do because
> the default behaviour is exactly this.

Ok makes sense. Will fix.

Thanks,
Vikas
> Thanks,
>
> 	tglx