linux-kernel - Re: [PATCH] cpuidle: do not shrink guest poll_limit_ns below grow

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Date: Mon, 12 Feb 2024 17:03:59 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Marcelo Tosatti <mtosatti@...hat.com>, Parshuram Sangle <parshuram.sangle@...el.com>
Cc: rafael@...nel.org, daniel.lezcano@...aro.org, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, jaishankar.rajendran@...el.com
Subject: Re: [PATCH] cpuidle: do not shrink guest poll_limit_ns below grow_start

On Thu, Feb 1, 2024 at 8:56 PM Marcelo Tosatti <mtosatti@...hat.com> wrote:
>
> On Thu, Jan 11, 2024 at 07:29:50PM +0530, Parshuram Sangle wrote:
> > While adjusting guest halt poll limit, grow block starts at
> > guest_halt_poll_grow_start without taking intermediate values.
> > Similar behavior is expected while shrinking the value. This
> > avoids short interval values which are really not required.
> >
> > VCPU1 trace (guest_halt_poll_shrink equals 2):
> >
> > VCPU1 grow 10000
> > VCPU1 shrink 5000
> > VCPU1 shrink 2500
> > VCPU1 shrink 1250
> > VCPU1 shrink 625
> > VCPU1 shrink 312
> > VCPU1 shrink 156
> > VCPU1 shrink 78
> > VCPU1 shrink 39
> > VCPU1 shrink 19
> > VCPU1 shrink 9
> > VCPU1 shrink 4
> >
> > Similar change is done in KVM halt poll flow with below patch:
> > Link: https://lore.kernel.org/kvm/20211006133021.271905-3-sashal@kernelorg/
> >
> > Co-developed-by: Rajendran Jaishankar <jaishankar.rajendran@...el.com>
> > Signed-off-by: Rajendran Jaishankar <jaishankar.rajendran@...el.com>
> > Signed-off-by: Parshuram Sangle <parshuram.sangle@...el.com>
> > ---
> >  drivers/cpuidle/governors/haltpoll.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/cpuidle/governors/haltpoll.c b/drivers/cpuidle/governors/haltpoll.c
> > index 1dff3a52917d..663b7f164d20 100644
> > --- a/drivers/cpuidle/governors/haltpoll.c
> > +++ b/drivers/cpuidle/governors/haltpoll.c
> > @@ -98,10 +98,15 @@ static void adjust_poll_limit(struct cpuidle_device *dev, u64 block_ns)
> >               unsigned int shrink = guest_halt_poll_shrink;
> >
> >               val = dev->poll_limit_ns;
> > -             if (shrink == 0)
> > +             if (shrink == 0) {
> >                       val = 0;
> > -             else
> > +             } else {
> >                       val /= shrink;
> > +                     /* Reset value to 0 if shrunk below grow_start */
> > +                     if (val < guest_halt_poll_grow_start)
> > +                             val = 0;
> > +             }
> > +
> >               trace_guest_halt_poll_ns_shrink(val, dev->poll_limit_ns);
> >               dev->poll_limit_ns = val;
> >       }
> > --
> > 2.17.1
> >
> >
> >
>
> Looks good.
>
> Reviewed-by: Marcelo Tosatti <mtosatti@...hat.com>

Applied as 6.9 (with a minor change in the subject), thanks!