linux-kernel - Re: [PATCH] cpuidle: powernv/pseries: Decrease the snooze residency

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Date:	Fri, 29 May 2015 19:17:17 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org
CC:	linux-pm@...r.kernel.org,
	Daniel Lezcano <daniel.lezcano@...aro.org>, rjw@...ysocki.net,
	linux-kernel@...r.kernel.org, anton@...ba.org
Subject: Re: [PATCH] cpuidle: powernv/pseries: Decrease the snooze residency

Hi Shilpa,

The subject does not convey the purpose of this patch clearly IMO.
I would definitely suggest changing the subject to something like
"Auto promotion of snooze to deeper idle state" or similar.

On 05/29/2015 06:02 PM, Shilpasri G Bhat wrote:
> The idle cpus which stay in snooze for a long period can degrade the
> perfomance of the sibling cpus. If the cpu stays in snooze for more
> than target residency of the next available idle state, then exit from
> snooze. This gives a chance to the cpuidle governor to re-evaluate the
> last idle state of the cpu to promote it to deeper idle states.
> 
> Signed-off-by: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
> ---
>  drivers/cpuidle/cpuidle-powernv.c | 12 ++++++++++++
>  drivers/cpuidle/cpuidle-pseries.c | 11 +++++++++++
>  2 files changed, 23 insertions(+)
> 
> diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c
> index bb9e2b6..07135e0 100644
> --- a/drivers/cpuidle/cpuidle-pseries.c
> +++ b/drivers/cpuidle/cpuidle-pseries.c
> @@ -27,6 +27,8 @@ struct cpuidle_driver pseries_idle_driver = {
>  
>  static int max_idle_state;
>  static struct cpuidle_state *cpuidle_state_table;
> +static u64 snooze_timeout;
> +static bool snooze_timeout_en;
>  
>  static inline void idle_loop_prolog(unsigned long *in_purr)
>  {
> @@ -58,14 +60,18 @@ static int snooze_loop(struct cpuidle_device *dev,
>  			int index)
>  {
>  	unsigned long in_purr;
> +	u64 snooze_exit_time;
>  
>  	idle_loop_prolog(&in_purr);
>  	local_irq_enable();
>  	set_thread_flag(TIF_POLLING_NRFLAG);
> +	snooze_exit_time = get_tb() + snooze_timeout;
>  
>  	while (!need_resched()) {
>  		HMT_low();
>  		HMT_very_low();
> +		if (snooze_timeout_en && get_tb() > snooze_exit_time)
> +			break;
>  	}
>  
>  	HMT_medium();
> @@ -244,6 +250,11 @@ static int pseries_idle_probe(void)
>  	} else
>  		return -ENODEV;
>  
> +	if (max_idle_state > 1) {
> +		snooze_timeout_en = true;
> +		snooze_timeout = cpuidle_state_table[1].target_residency *
> +				 tb_ticks_per_usec;
> +	}

Any idea why we don't have snooze defined on the shared lpar configuration ?

Regards
Preeti U Murthy
>  	return 0;
>  }
>  
> 

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