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Message-ID: <20080923101938.GE4598@in.ibm.com>
Date: Tue, 23 Sep 2008 15:49:38 +0530
From: Gautham R Shenoy <ego@...ibm.com>
To: Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Suresh Siddha <suresh.b.siddha@...el.com>
Cc: linux-kernel@...r.kernel.org,
Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
Srivatsa Vaddagiri <vatsa@...ibm.com>,
Balbir Singh <balbir@...ibm.com>
Subject: [PATCH] sched: Nominate the idle load balancer from a semi-idle
group.
sched: Nominate the idle load balancer from a semi-idle group.
From: Gautham R Shenoy <ego@...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@...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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