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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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