Re: [PATCH] interconnect: Skip call into provider if initial bw is zero

[Vivek Aknurwar]

Hi Bryan,
Thanks for taking time to review the patch.

On 1/13/2023 5:40 PM, Bryan O'Donoghue wrote:
> On 14/01/2023 01:24, Bryan O'Donoghue wrote:
> > On 13/01/2023 22:07, Vivek Aknurwar wrote:
> > > Currently framework sets bw even when init bw requirements are zero 
> > > during
> > > provider registration, thus resulting bulk of set bw to hw.
> > > Avoid this behaviour by skipping provider set bw calls if init bw is 
> > > zero.
> > >
> > > Signed-off-by: Vivek Aknurwar <quic_viveka@xxxxxxxxxxx>
> > > ---
> > >   drivers/interconnect/core.c | 17 ++++++++++-------
> > >   1 file changed, 10 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
> > > index 25debde..43ed595 100644
> > > --- a/drivers/interconnect/core.c
> > > +++ b/drivers/interconnect/core.c
> > > @@ -977,14 +977,17 @@ void icc_node_add(struct icc_node *node, struct 
> > > icc_provider *provider)
> > >       node->avg_bw = node->init_avg;
> > >       node->peak_bw = node->init_peak;
> > > -    if (provider->pre_aggregate)
> > > -        provider->pre_aggregate(node);
> > > -
> > > -    if (provider->aggregate)
> > > -        provider->aggregate(node, 0, node->init_avg, node->init_peak,
> > > -                    &node->avg_bw, &node->peak_bw);
> > > +    if (node->avg_bw || node->peak_bw) {
> > > +        if (provider->pre_aggregate)
> > > +            provider->pre_aggregate(node);
> > > +
> > > +        if (provider->aggregate)
> > > +            provider->aggregate(node, 0, node->init_avg, 
> > > node->init_peak,
> > > +                        &node->avg_bw, &node->peak_bw);
> > > +        if (provider->set)
> > > +            provider->set(node, node);
> > > +    }
> > > -    provider->set(node, node);
> > >       node->avg_bw = 0;
> > >       node->peak_bw = 0;
> >
> > I have the same comment/question for this patch that I had for the 
> > qcom arch specific version of it. This patch seems to be doing at a 
> > higher level what the patch below was doing at a lower level.
> >
> > https://lore.kernel.org/lkml/1039a507-c4cd-e92f-dc29-1e2169ce5078@xxxxxxxxxx/T/#m0c90588d0d1e2ab88c39be8f5f3a8f0b61396349
> >
> > what happens to earlier silicon - qcom silicon which previously made 
> > explicit zero requests ?

This patch is to optimize and avoid all those bw 0 requests on each node 
addition during probe (which results in rpmh remote calls) for upcoming 
targets.

> > https://lore.kernel.org/lkml/1039a507-c4cd-e92f-dc29-1e2169ce5078@xxxxxxxxxx/T/#m589e8280de470e038249bb362634221771d845dd
> >
> > https://lkml.org/lkml/2023/1/3/1232
> >
> > Isn't it a better idea to let lower layer drivers differentiate what 
> > they do ?

AFAIU lower layer driver can/should not differentiate between normal 
flow calls vs made as a result from probe/initialization of driver. 
Hence even bw 0 request is honored as like client in general wish to 
vote 0 as in an normal use case.

> > For example on pre 5.4 qcom kernel silicon we might choose to set the 
> > value to zero "because that's what the reference code did" but on 
> > newer silicon we might opt to skip the zero configuration ?
> >
> > I'm happy to be shown the error of my ways but, absent testing to 
> > *show* it doesn't impact existing legacy silicon, I think we should be 
> > wary of this change.
> >
> > ---
> > bod
>
> Oh, and what is the effect on Samsung and i.MX silicon interconnect 
> providers of skipping the zero set ?

If interconnect providers are trying to clear bw votes coming from 
boot-loader then best place to clear those is in sync-state call back.

> ---
> bod