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

[Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>]

* Balbir Singh <balbir@linux.vnet.ibm.com> [2008-12-12 00:25:29]:

> * 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

Hi Balbir,

Good catch.  I have always been providing correct value ;)

An incorrect input will make sched_mc=0  I just verified that.  I will
fix it.

--Vaidy