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


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