Re: [RFC PATCH v5 1/7] sched: Framework for sched_mc/smt_power_savings=N

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> [2008-12-11 23:12:37]:

> From: Gautham R Shenoy <ego@in.ibm.com>
> 
> ***  RFC patch of work in progress and not for inclusion. ***
> 
> Currently the sched_mc/smt_power_savings variable is a boolean, which either
> enables or disables topology based power savings. This extends the behaviour of
> the variable from boolean to multivalued, such that based on the value, we
> decide how aggressively do we want to perform topology based powersavings
> balance.
> 
> Variable levels of power saving tunable would benefit end user to match the
> required level of power savings vs performance trade off depending on the
> system configuration and workloads.
> 
> This initial version makes the sched_mc_power_savings global variable to take
> more values (0,1,2).
> 
> Later version is expected to add new member sd->powersavings_level at the multi
> core CPU level sched_domain. This make all sd->flags check for
> SD_POWERSAVINGS_BALANCE into a different macro that will check for
> powersavings_level.
> 
> The power savings level setting should be in one place either in the
> sched_mc_power_savings global variable or contained within the appropriate
> sched_domain structure.
> 
> Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
> Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
> ---
> 
>  include/linux/sched.h |   11 +++++++++++
>  kernel/sched.c        |   16 +++++++++++++---
>  2 files changed, 24 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 55e30d1..888f2b2 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -764,6 +764,17 @@ enum cpu_idle_type {
>  #define SD_SERIALIZE		1024	/* Only a single load balancing instance */
>  #define SD_WAKE_IDLE_FAR	2048	/* Gain latency sacrificing cache hit */
> 
> +enum powersavings_balance_level {
> +	POWERSAVINGS_BALANCE_NONE = 0,  /* No power saving load balance */
> +	POWERSAVINGS_BALANCE_BASIC,	/* Fill one thread/core/package
> +					 * first for long running threads
> +					 */
> +	POWERSAVINGS_BALANCE_WAKEUP,	/* Also bias task wakeups to semi-idle
> +					 * cpu package for power savings
> +					 */
> +	MAX_POWERSAVINGS_BALANCE_LEVELS
> +};
> +
>  #define BALANCE_FOR_MC_POWER	\
>  	(sched_smt_power_savings ? SD_POWERSAVINGS_BALANCE : 0)
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index e4bb1dd..322cd2a 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -7879,14 +7879,24 @@ int arch_reinit_sched_domains(void)
>  static ssize_t sched_power_savings_store(const char *buf, size_t count, int smt)
>  {
>  	int ret;
> +	unsigned int level = 0;
> 
> -	if (buf[0] != '0' && buf[0] != '1')
> +	sscanf(buf, "%u", &level);

Don't we need to check what sscanf returns? Does a invalid value push
the power savings to 0

> +
> +	/*
> +	 * level is always be positive so don't check for
> +	 * level < POWERSAVINGS_BALANCE_NONE which is 0
> +	 * What happens on 0 or 1 byte write,
> +	 * need to check for count as well?
> +	 */

See above

> +
> +	if (level >= MAX_POWERSAVINGS_BALANCE_LEVELS)
>  		return -EINVAL;
> 
>  	if (smt)
> -		sched_smt_power_savings = (buf[0] == '1');
> +		sched_smt_power_savings = level;
>  	else
> -		sched_mc_power_savings = (buf[0] == '1');
> +		sched_mc_power_savings = level;
> 
>  	ret = arch_reinit_sched_domains();
> 
> 
> 

-- 
	Balbir