| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Tue, 03 Mar 2009 17:21:49 +0530
From: Gautham R Shenoy <ego@...ibm.com>
To: "Vaidyanathan Srinivasan" <svaidy@...ux.vnet.ibm.com>,
"Balbir Singh" <balbir@...ibm.com>,
"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
"Ingo Molnar" <mingo@...e.hu>,
"Suresh Siddha" <suresh.b.siddha@...el.com>
Cc: "Dipankar Sarma" <dipankar@...ibm.com>, efault@....de,
andi@...stfloor.org, linux-kernel@...r.kernel.org,
Gautham R Shenoy <ego@...ibm.com>,
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: [PATCH 2 2/3] sched: Fix the wakeup nomination for
sched_mc/smt_power_savings.
The existing algorithm to nominate a preferred wake up cpu would not
work on a machine which has both sched_mc_power_savings and
sched_smt_power_savings enabled. On such machines, the nomination at a lower
level would keep overwriting the nominations by it's peer-level as well as
higher level sched_domains. This would lead to the ping-ponging of the
nominated wake-up cpu, thereby preventing us from effectively consolidating
tasks.
Correct this by defining the authorized nomination sched_domain level, which
is either the highest sched_domain level containing the
SD_POWERSAVINGS_BALANCE flag or a lower level which contains the previously
nominated wake-up cpu in it's span.
Signed-off-by: Gautham R Shenoy <ego@...ibm.com>
Cc: Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
---
include/linux/sched.h | 1 +
kernel/sched.c | 74 +++++++++++++++++++++++++++++++++++++++++++++----
kernel/sched_fair.c | 2 +
3 files changed, 70 insertions(+), 7 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 362807a..7f66595 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -776,6 +776,7 @@ enum powersavings_balance_level {
};
extern int sched_mc_power_savings, sched_smt_power_savings;
+extern enum powersavings_balance_level active_power_savings_level;
enum sched_domain_level {
SD_LV_NONE = 0,
diff --git a/kernel/sched.c b/kernel/sched.c
index 52bbf1c..7d22a96 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -515,11 +515,22 @@ struct root_domain {
#endif
#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
/*
- * Preferred wake up cpu nominated by sched_mc balance that will be
- * used when most cpus are idle in the system indicating overall very
- * low system utilisation. Triggered at POWERSAVINGS_BALANCE_WAKEUP(2)
+ * Preferred wake up cpu which is nominated by load balancer,
+ * is the CPU on which the tasks would be woken up, which
+ * otherwise would have woken up on an idle CPU even on a system
+ * with low-cpu-utilization.
+ * This is triggered at POWERSAVINGS_BALANCE_WAKEUP(2).
*/
unsigned int sched_mc_preferred_wakeup_cpu;
+ /*
+ * authorized_nomination_level records the sched-domain level, which can
+ * in the process of load-balancing nominate the
+ * sched_mc_preferred_wakeup_cpu.
+ *
+ * This helps in serializing the nominations thereby preventing
+ * multiple sched-domain levels overwriting each others' nominations.
+ */
+ enum sched_domain_level authorized_nomination_level;
#endif
};
@@ -3090,6 +3101,22 @@ static int move_one_task(struct rq *this_rq, int this_cpu, struct rq *busiest,
* find_busiest_group finds and returns the busiest CPU group within the
* domain. It calculates and returns the amount of weighted load which
* should be moved to restore balance via the imbalance parameter.
+ *
+ * Power-savings-balance: If the user has enabled the option to save power
+ * by means of task consolidation, then at the corresponding sched_domains,
+ * the SD_POWERSAVINGS_BALANCE flag will be set.
+ *
+ * Within such sched_domains, find_busiest_group would try to identify
+ * a sched_group which can be freed-up and it's tasks can be migrated to
+ * another group which has the capacity to accomodate the former's tasks.
+ * If such a "can-go-idle" sched_groups does exist, then the group which can
+ * accomodate it's tasks is returned as the busiest group.
+ *
+ * Furthermore, if the user opts for more aggressive power-aware load
+ * balancing, i.e when the active_power_savings_level greater or equal to
+ * POWERSAVINGS_BALANCE_WAKEUP, find_busiest_group will also nominate
+ * the preferred CPU, on which the tasks should hence forth
+ * be woken up on, instead of bothering an idle-cpu.
*/
static struct sched_group *
find_busiest_group(struct sched_domain *sd, int this_cpu,
@@ -3397,9 +3424,18 @@ out_balanced:
goto ret;
if (this == group_leader && group_leader != group_min) {
+ struct root_domain *my_rd = cpu_rq(this_cpu)->rd;
*imbalance = min_load_per_task;
- if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP) {
- cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu =
+ /*
+ * Nominate the the preferred wakeup cpu only if this
+ * sched_domain is authorized to do so, or if this sched_domain
+ * contains the previously nominated cpu.
+ */
+ if (sd->level == my_rd->authorized_nomination_level ||
+ (sd->level < my_rd->authorized_nomination_level &&
+ cpu_isset(my_rd->sched_mc_preferred_wakeup_cpu,
+ *sched_domain_span(sd)))) {
+ my_rd->sched_mc_preferred_wakeup_cpu =
cpumask_first(sched_group_cpus(group_leader));
}
return group_min;
@@ -3683,7 +3719,8 @@ redo:
!test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
return -1;
- if (sched_mc_power_savings < POWERSAVINGS_BALANCE_WAKEUP)
+ if (active_power_savings_level <
+ POWERSAVINGS_BALANCE_WAKEUP)
return -1;
if (sd->nr_balance_failed++ < 2)
@@ -7193,6 +7230,9 @@ static void sched_domain_node_span(int node, struct cpumask *span)
int sched_smt_power_savings = 0, sched_mc_power_savings = 0;
+/* Records the currently active power saving level. */
+enum powersavings_balance_level active_power_savings_level;
+
/*
* The cpus mask in sched_group and sched_domain hangs off the end.
* FIXME: use cpumask_var_t or dynamic percpu alloc to avoid wasting space
@@ -7781,6 +7821,25 @@ static int __build_sched_domains(const struct cpumask *cpu_map,
err = 0;
+/* Assign the sched-domain level which can nominate preferred wake-up cpu */
+ rd->sched_mc_preferred_wakeup_cpu = UINT_MAX;
+ rd->authorized_nomination_level = SD_LV_NONE;
+
+ if (active_power_savings_level >= POWERSAVINGS_BALANCE_WAKEUP) {
+ struct sched_domain *sd;
+ enum sched_domain_level authorized_nomination_level =
+ SD_LV_NONE;
+
+ for_each_domain(first_cpu(*cpu_map), sd) {
+ if (!(sd->flags & SD_POWERSAVINGS_BALANCE))
+ continue;
+ authorized_nomination_level = sd->level;
+ }
+
+ rd->authorized_nomination_level = authorized_nomination_level;
+ }
+
+
free_tmpmask:
free_cpumask_var(tmpmask);
free_send_covered:
@@ -8027,6 +8086,9 @@ static ssize_t sched_power_savings_store(const char *buf, size_t count, int smt)
else
sched_mc_power_savings = level;
+ active_power_savings_level = max(sched_smt_power_savings,
+ sched_mc_power_savings);
+
arch_reinit_sched_domains();
return count;
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 5cc1c16..bddee3e 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1042,7 +1042,7 @@ static int wake_idle(int cpu, struct task_struct *p)
chosen_wakeup_cpu =
cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu;
- if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP &&
+ if (active_power_savings_level >= POWERSAVINGS_BALANCE_WAKEUP &&
idle_cpu(cpu) && idle_cpu(this_cpu) &&
p->mm && !(p->flags & PF_KTHREAD) &&
cpu_isset(chosen_wakeup_cpu, p->cpus_allowed))
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists