Re: [PATCH] cpuidle: do not shrink guest poll_limit_ns below grow_start

From: Rafael J. Wysocki
Date: Mon Feb 12 2024 - 11:04:23 EST


On Thu, Feb 1, 2024 at 8:56 PM Marcelo Tosatti <mtosatti@xxxxxxxxxx> 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@xxxxxxxxx>
> > Signed-off-by: Rajendran Jaishankar <jaishankar.rajendran@xxxxxxxxx>
> > Signed-off-by: Parshuram Sangle <parshuram.sangle@xxxxxxxxx>
> > ---
> > 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@xxxxxxxxxx>

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