Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENTfor power oriented workqueues

[Viresh Kumar]

On 25 April 2013 09:00, Amit Kucheria <amit.kucheria@xxxxxxxxxx> wrote:
> Yes. That was my intention - preventing a prompt on existing defconfigs and
> there by maintaining current behavior.

Hmm... Following is the version after fixing all problems you reported.
@Tejun: I have attached it too as gmail's copy-paste may break it. Please
consider applying this series if it looks fine to you.


---------------x----------------x---------------------

From: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
Date: Mon, 8 Apr 2013 16:45:40 +0530
Subject: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for
 power oriented workqueues

Workqueues can be performance or power-oriented. Currently, most workqueues are
bound to the CPU they were created on. This gives good performance (due to cache
effects) at the cost of potentially waking up otherwise idle cores just to
process some work. To save power, we can allow the work to be rescheduled on a
core that is already awake.

Workqueues created with the WQ_UNBOUND flag will allow some power savings.
However, we don't change the default behaviour of the system.  To enable
power-saving behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT needs to
be turned on. This option can also be overridden by the
workqueue.power_efficient boot parameter.

Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
 Documentation/kernel-parameters.txt | 17 +++++++++++++++++
 include/linux/workqueue.h           |  3 +++
 kernel/power/Kconfig                | 19 +++++++++++++++++++
 kernel/workqueue.c                  | 11 +++++++++++
 4 files changed, 50 insertions(+)

diff --git a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt
index c4fa000..22edc83 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3312,6 +3312,23 @@ 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
+			Workqueues can be performance or power-oriented.
+			Currently, most workqueues are bound to the CPU they
+			were created on. This gives good performance (due to
+			cache effects) at the cost of potentially waking up
+			otherwise idle cores just to process some work. To save
+			power, we can allow the work to be rescheduled on a core
+			that is already awake.
+
+			Workqueues created with the WQ_UNBOUND flag will allow
+			some power savings.  However, we don't change the
+			default behaviour of the system.  To enable power-saving
+			behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT
+			needs to be turned on. This option can also be
+			overridden by the workqueue.power_efficient boot
+			parameter.
+
 	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..83fa570 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -302,6 +302,9 @@ enum {
 	WQ_HIGHPRI		= 1 << 4, /* high priority */
 	WQ_CPU_INTENSIVE	= 1 << 5, /* cpu instensive workqueue */
 	WQ_SYSFS		= 1 << 6, /* visible in sysfs, see wq_sysfs_register() */
+	WQ_POWER_EFFICIENT	= 1 << 7, /* WQ_UNBOUND, for power
+					   * saving, if wq_power_efficient is
+					   * enabled. Unused otherwise. */

 	__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..018f039 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -263,6 +263,25 @@ config PM_GENERIC_DOMAINS
 	bool
 	depends on PM

+config WQ_POWER_EFFICIENT
+	bool "Workqueue allocated as UNBOUND (by default) for power efficiency"
+	depends on PM
+	default n
+	help
+	  Workqueues can be performance or power-oriented. Currently, most
+	  workqueues are bound to the CPU they were created on. This gives good
+	  performance (due to cache effects) at the cost of potentially waking
+	  up otherwise idle cores just to process some work. To save power, we
+	  can allow the work to be rescheduled on a core that is already awake.
+
+	  Workqueues created with the WQ_UNBOUND flag will allow some power
+	  savings.  However, we don't change the default behaviour of the
+	  system.  To enable power-saving behaviour, a new config option
+	  CONFIG_WQ_POWER_EFFICIENT needs to be turned on. This option can also
+	  be overridden by the workqueue.power_efficient boot parameter.
+
+	  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..a327027 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -272,6 +272,14 @@ static cpumask_var_t *wq_numa_possible_cpumask;
 static bool wq_disable_numa;
 module_param_named(disable_numa, wq_disable_numa, bool, 0444);

+#ifdef CONFIG_WQ_POWER_EFFICIENT
+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 +4093,9 @@ struct workqueue_struct
*__alloc_workqueue_key(const char *fmt,
 	struct workqueue_struct *wq;
 	struct pool_workqueue *pwq;

+	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]);

Attachment: 0001-workqueues-Introduce-new-flag-WQ_POWER_EFFICIENT-for.patch
Description: Binary data