Messages in this thread Patch in this message | | | Date | Tue, 23 Sep 2008 15:49:38 +0530 | From | Gautham R Shenoy <> | Subject | [PATCH] sched: Nominate the idle load balancer from a semi-idle group. |
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sched: Nominate the idle load balancer from a semi-idle group.
From: Gautham R Shenoy <ego@in.ibm.com>
Currently the first cpu in the nohz cpu mask is nominated as the idle load balancer.
However, this could be a cpu from an idle group, thereby not yiedling the expected power savings.
Improve the logic to pick an idle cpu from a semi-idle group for performing the task of idle load balancing, when sched_mc/smt_powersavings is enabled.
This patch has no effect when sched_mc/smt_powersavings is turned off.
The patch is based on linux-2.6.27-rc5 and depends on the fix for sched_mc_powersavings posted here--> http://lkml.org/lkml/2008/9/5/135
SPEC-Power Results: on a large multi-socket multi-core x86. ---------------------------------------------------------------- Summary with the patch: 9% improvement in the overall score 8% decrease in the Power consumption at 100% utilization. 12% decrease in the Power consumption at idle.
---------------------------------------------------------------- kernel_version |Final Score |ssj ops | 100% Watts | Idle Watts | ---------------|------------|--------|-------------------------| 2.6.27-rc5 | x | y | z | w | ---------------|------------|--------|------------|------------| 2.6.27-rc5 + | 1.05x | 0.98y | 0.94z | 0.92w | sched_mc_fix | | | | | ---------------|------------|--------|------------|------------| 2.6.27-rc5 + | 1.09x | 0.97y | 0.92z | 0.88w | sched_mc_fix + | | | | | this_patch | | | | | ----------------------------------------------------------------
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com> ---
kernel/sched.c | 86 ++++++++++++++++++++++++++++++++++++++++++++++++++------ 1 files changed, 77 insertions(+), 9 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c index cc1f81b..c186719 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -3960,6 +3960,82 @@ static void run_rebalance_domains(struct softirq_action *h) #endif } +#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT) +/** + * lowest_powersavings_sd: Returns the lowest level of power savings + * domain of the given cpu. + * @cpu: The cpu whose lowest level of power savings domain to + * be returned. + * + * Power savings domain is the sched_domain where in we perform + * load balancing for power savings. Such a domain would have + * SD_POWERSAVINGS_BALANCE bit set in it's flags. + */ +static inline struct sched_domain *lowest_powersavings_sd(int cpu) +{ + struct sched_domain *sd; + + for_each_domain(cpu, sd) + if (sd && (sd->flags & SD_POWERSAVINGS_BALANCE)) + break; + + return sd; +} + +/** + * for_each_powersavings_domain: Iterates over all the power savings + * scheduler domains (see comment for lowest_powersavings_sd) from + * the lowest to the highest. + * @cpu: The cpu whose powersavings_sd we're iterating over. + * @sd: variable holding the value of the power_savings_sd + * for cpu + */ +#define for_each_powersaving_domain(cpu, sd) \ + for (sd = lowest_powersavings_sd(cpu); \ + (sd && (sd->flags & SD_POWERSAVINGS_BALANCE)); sd = sd->parent) +/** + * find_new_ilb: Finds or nominates a new idle load balancer. + * @cpu: The cpu which is nominating a new idle_load_balancer. + * + * This algorithm picks the idle load balancer such that it belongs to a + * semi-idle powersavings sched_domain. The idea is to try and avoid + * completely idle packages/cores just for the purpose of idle load balancing + * when there are other idle cpu's which are better suited for that job. + */ +static int find_new_ilb(int cpu) +{ + struct sched_domain *sd; + struct sched_group *ilb_group; + cpumask_t cpumask; + + for_each_powersaving_domain(cpu, sd) { + ilb_group = sd->groups; + + do { + cpus_and(cpumask, nohz.cpu_mask, ilb_group->cpumask); + + /* + * If there exists atleast one busy cpu within + * this group, we should wake up the idle cpu from + * here. + */ + if (!(cpus_empty(cpumask) || + cpus_equal(cpumask, ilb_group->cpumask))) + return first_cpu(cpumask); + + ilb_group = ilb_group->next; + + } while (ilb_group != sd->groups); + } + return first_cpu(nohz.cpu_mask); +} +#else /* (CONFIG_SCHED_MC || CONFIG_SCHED_SMT) */ +static inline int find_new_ilb(int call_cpu) +{ + return first_cpu(nohz.cpu_mask); +} +#endif + /* * Trigger the SCHED_SOFTIRQ if it is time to do periodic load balancing. * @@ -3984,15 +4060,7 @@ static inline void trigger_load_balance(struct rq *rq, int cpu) } if (atomic_read(&nohz.load_balancer) == -1) { - /* - * simple selection for now: Nominate the - * first cpu in the nohz list to be the next - * ilb owner. - * - * TBD: Traverse the sched domains and nominate - * the nearest cpu in the nohz.cpu_mask. - */ - int ilb = first_cpu(nohz.cpu_mask); + int ilb = find_new_ilb(cpu); if (ilb < nr_cpu_ids) resched_cpu(ilb); -- Thanks and Regards gautham
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