linux-kernel - Re: [PATCH] cpuidle: riscv-sbi: Add cluster_pm

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Message-ID: <CAKddAkDcdaXKzpcKN=LCCx9S4Trv+joLX2s=nyhzaRtM5HorqA@mail.gmail.com>
Date: Tue, 30 Apr 2024 00:22:25 +0800
From: Nick Hu <nick.hu@...ive.com>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: palmer@...belt.com, anup@...infault.org, rafael@...nel.org, 
	daniel.lezcano@...aro.org, paul.walmsley@...ive.com, linux-pm@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	zong.li@...ive.com
Subject: Re: [PATCH] cpuidle: riscv-sbi: Add cluster_pm_enter()/exit()

Hi Ulf

On Mon, Apr 29, 2024 at 10:32 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On Mon, 26 Feb 2024 at 07:51, Nick Hu <nick.hu@...ive.com> wrote:
> >
> > When the cpus in the same cluster are all in the idle state, the kernel
> > might put the cluster into a deeper low power state. Call the
> > cluster_pm_enter() before entering the low power state and call the
> > cluster_pm_exit() after the cluster woken up.
> >
> > Signed-off-by: Nick Hu <nick.hu@...ive.com>
>
> I was not cced this patch, but noticed that this patch got queued up
> recently. Sorry for not noticing earlier.
>
> If not too late, can you please drop/revert it? We should really move
> away from the CPU cluster notifiers. See more information below.
>
> > ---
> >  drivers/cpuidle/cpuidle-riscv-sbi.c | 24 ++++++++++++++++++++++--
> >  1 file changed, 22 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/cpuidle/cpuidle-riscv-sbi.c b/drivers/cpuidle/cpuidle-riscv-sbi.c
> > index e8094fc92491..298dc76a00cf 100644
> > --- a/drivers/cpuidle/cpuidle-riscv-sbi.c
> > +++ b/drivers/cpuidle/cpuidle-riscv-sbi.c
> > @@ -394,6 +394,7 @@ static int sbi_cpuidle_pd_power_off(struct generic_pm_domain *pd)
> >  {
> >         struct genpd_power_state *state = &pd->states[pd->state_idx];
> >         u32 *pd_state;
> > +       int ret;
> >
> >         if (!state->data)
> >                 return 0;
> > @@ -401,6 +402,10 @@ static int sbi_cpuidle_pd_power_off(struct generic_pm_domain *pd)
> >         if (!sbi_cpuidle_pd_allow_domain_state)
> >                 return -EBUSY;
> >
> > +       ret = cpu_cluster_pm_enter();
> > +       if (ret)
> > +               return ret;
>
> Rather than using the CPU cluster notifiers, consumers of the genpd
> can register themselves to receive genpd on/off notifiers.
>
> In other words, none of this should be needed, right?
>
Thanks for the feedback!
Maybe I miss something, I'm wondering about a case like below:
If we have a shared L2 cache controller inside the cpu cluster power
domain and we add this controller to be a consumer of the power
domain, Shouldn't the genpd invoke the domain idle only after the
shared L2 cache controller is suspended?
Is there a way that we can put the L2 cache down while all cpus in the
same cluster are idle?
> [...]
>
> Kind regards
> Uffe