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

[Marcelo Tosatti <mtosatti@redhat.com>]

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@kernel.org/
> 
> Co-developed-by: Rajendran Jaishankar <jaishankar.rajendran@intel.com>
> Signed-off-by: Rajendran Jaishankar <jaishankar.rajendran@intel.com>
> Signed-off-by: Parshuram Sangle <parshuram.sangle@intel.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@redhat.com>