summaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
-rw-r--r--Documentation/kernel-parameters.txt15
-rw-r--r--include/linux/workqueue.h27
-rw-r--r--kernel/power/Kconfig20
-rw-r--r--kernel/workqueue.c13
4 files changed, 75 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index c3bfacb..37dfd72 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3320,6 +3320,21 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
that this also can be controlled per-workqueue for
workqueues visible under /sys/bus/workqueue/.
+ workqueue.power_efficient
+ Per-cpu workqueues are generally preferred because
+ they show better performance thanks to cache
+ locality; unfortunately, per-cpu workqueues tend to
+ be more power hungry than unbound workqueues.
+
+ Enabling this makes the per-cpu workqueues which
+ were observed to contribute significantly to power
+ consumption unbound, leading to measurably lower
+ power usage at the cost of small performance
+ overhead.
+
+ The default value of this parameter is determined by
+ the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
+
x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
default x2apic cluster mode on platforms
supporting x2apic.
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 623488f..fc0136b 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -303,6 +303,33 @@ enum {
WQ_CPU_INTENSIVE = 1 << 5, /* cpu instensive workqueue */
WQ_SYSFS = 1 << 6, /* visible in sysfs, see wq_sysfs_register() */
+ /*
+ * Per-cpu workqueues are generally preferred because they tend to
+ * show better performance thanks to cache locality. Per-cpu
+ * workqueues exclude the scheduler from choosing the CPU to
+ * execute the worker threads, which has an unfortunate side effect
+ * of increasing power consumption.
+ *
+ * The scheduler considers a CPU idle if it doesn't have any task
+ * to execute and tries to keep idle cores idle to conserve power;
+ * however, for example, a per-cpu work item scheduled from an
+ * interrupt handler on an idle CPU will force the scheduler to
+ * excute the work item on that CPU breaking the idleness, which in
+ * turn may lead to more scheduling choices which are sub-optimal
+ * in terms of power consumption.
+ *
+ * Workqueues marked with WQ_POWER_EFFICIENT are per-cpu by default
+ * but become unbound if workqueue.power_efficient kernel param is
+ * specified. Per-cpu workqueues which are identified to
+ * contribute significantly to power-consumption are identified and
+ * marked with this flag and enabling the power_efficient mode
+ * leads to noticeable power saving at the cost of small
+ * performance disadvantage.
+ *
+ * http://thread.gmane.org/gmane.linux.kernel/1480396
+ */
+ WQ_POWER_EFFICIENT = 1 << 7,
+
__WQ_DRAINING = 1 << 16, /* internal: workqueue is draining */
__WQ_ORDERED = 1 << 17, /* internal: workqueue is ordered */
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 5dfdc9e..4645596 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -263,6 +263,26 @@ config PM_GENERIC_DOMAINS
bool
depends on PM
+config WQ_POWER_EFFICIENT_DEFAULT
+ bool "Enable workqueue power-efficient mode by default"
+ depends on PM
+ default n
+ help
+ Per-cpu workqueues are generally preferred because they show
+ better performance thanks to cache locality; unfortunately,
+ per-cpu workqueues tend to be more power hungry than unbound
+ workqueues.
+
+ Enabling workqueue.power_efficient kernel parameter makes the
+ per-cpu workqueues which were observed to contribute
+ significantly to power consumption unbound, leading to measurably
+ lower power usage at the cost of small performance overhead.
+
+ This config option determines whether workqueue.power_efficient
+ is enabled by default.
+
+ If in doubt, say N.
+
config PM_GENERIC_DOMAINS_SLEEP
def_bool y
depends on PM_SLEEP && PM_GENERIC_DOMAINS
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 4aa9f5b..8068d97 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -272,6 +272,15 @@ static cpumask_var_t *wq_numa_possible_cpumask;
static bool wq_disable_numa;
module_param_named(disable_numa, wq_disable_numa, bool, 0444);
+/* see the comment above the definition of WQ_POWER_EFFICIENT */
+#ifdef CONFIG_WQ_POWER_EFFICIENT_DEFAULT
+static bool wq_power_efficient = true;
+#else
+static bool wq_power_efficient;
+#endif
+
+module_param_named(power_efficient, wq_power_efficient, bool, 0444);
+
static bool wq_numa_enabled; /* unbound NUMA affinity enabled */
/* buf for wq_update_unbound_numa_attrs(), protected by CPU hotplug exclusion */
@@ -4085,6 +4094,10 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
struct workqueue_struct *wq;
struct pool_workqueue *pwq;
+ /* see the comment above the definition of WQ_POWER_EFFICIENT */
+ if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient)
+ flags |= WQ_UNBOUND;
+
/* allocate wq and format name */
if (flags & WQ_UNBOUND)
tbl_size = wq_numa_tbl_len * sizeof(wq->numa_pwq_tbl[0]);
OpenPOWER on IntegriCloud