Re: [PATCH v3 21/21] x86/resctrl: Make resctrl_arch_rmid_read() return values in bytes

[James Morse]

Hi Rob,

On 3/23/22 21:17, Rob Herring wrote:
> On Thu, Feb 17, 2022 at 06:21:10PM +0000, James Morse wrote:
> > resctrl_arch_rmid_read() returns a value in chunks, as read from the
> > hardware. This needs scaling to bytes by mon_scale, as provided by
> > the architecture code.
> >
> > Now that resctrl_arch_rmid_read() performs the overflow and corrections
> > itself, it may as well return a value in bytes directly. This allows
> > the accesses to the architecture specific 'hw' structure to be removed.
> >
> > Move the mon_scale conversion into resctrl_arch_rmid_read().
> > mbm_bw_count() is updated to calculate bandwidth from bytes.

> > diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> > index 3a6555f49720..437e7db77f93 100644
> > --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> > +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> > @@ -211,10 +211,11 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
> >   	if (am) {
> >   		am->chunks += mbm_overflow_count(am->prev_msr, msr_val,
> >   						 hw_res->mbm_width);
> > -		*val = get_corrected_mbm_count(rmid, am->chunks);
> > +		chunks = get_corrected_mbm_count(rmid, am->chunks);
> > +		*val = chunks * hw_res->mon_scale;
>
> This can be moved out of the if/else if you make the following change:
>
> >   		am->prev_msr = msr_val;
> >   	} else {
> > -		*val = msr_val;
> > +		*val = msr_val * hw_res->mon_scale;
>
> chunks = msr_val;
>
> >   	}

Sure, I guess it makes sense to only set *val in one place.

> >   
> >   	return 0;
> > @@ -400,15 +397,14 @@ static u64 __mon_event_count(u32 rmid, struct rmid_read *rr)
> >    */
> >   static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
> >   {
> > -	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(rr->r);
> >   	struct mbm_state *m = &rr->d->mbm_local[rmid];
> > -	u64 cur_bw, chunks, cur_chunks;
> > +	u64 cur_bw, bytes, cur_bytes;
> >   
> > -	cur_chunks = rr->val;
> > -	chunks = cur_chunks - m->prev_bw_chunks;
> > -	m->prev_bw_chunks = cur_chunks;
> > +	cur_bytes = rr->val;
> > +	bytes = cur_bytes - m->prev_bw_bytes;
> > +	m->prev_bw_bytes = cur_bytes;
> >   
> > -	cur_bw = (chunks * hw_res->mon_scale) >> 20;
> > +	cur_bw = bytes >> 20;
>
> 'bytes / SZ_1M' would be more readable and any decent compiler should
> optimize a power of 2 divide. But maybe that's a separate change as
> there are other cases of bytes to MB.

I agree its more readable. As I've touched this one, I'll change it.


Thanks,

James