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 (Idle from scheduler's perspective. Which may or may not be physically idle) 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. tj: Updated config description and comments. Renamed CONFIG_WQ_POWER_EFFICIENT to CONFIG_WQ_POWER_EFFICIENT_DEFAULT.

Viresh Kumar committed 13 years ago

Commit cee22a11 parent f7224064 files · +75 −0Browse files

Showing the changes to kernel/workqueue.c (1 of 4 files). Show all

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kernel/workqueue.c+13−0

@@ -272,6 +272,15 @@ static cpumask_var_t *wq_numa_possible_cpumask; · 271 unmodified lines
272	static bool wq_disable_numa;	272	static bool wq_disable_numa;
273	module_param_named(disable_numa, wq_disable_numa, bool, 0444);	273	module_param_named(disable_numa, wq_disable_numa, bool, 0444);
274		274
		275	/* see the comment above the definition of WQ_POWER_EFFICIENT */
		276	#ifdef CONFIG_WQ_POWER_EFFICIENT_DEFAULT
		277	static bool wq_power_efficient = true;
		278	#else
		279	static bool wq_power_efficient;
		280	#endif
		281
		282	module_param_named(power_efficient, wq_power_efficient, bool, 0444);
		283
275	static bool wq_numa_enabled; /* unbound NUMA affinity enabled */	284	static bool wq_numa_enabled; /* unbound NUMA affinity enabled */
276		285
277	/* buf for wq_update_unbound_numa_attrs(), protected by CPU hotplug exclusion */	286	/* 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, · 3807 unmodified lines
4085	struct workqueue_struct *wq;	4094	struct workqueue_struct *wq;
4086	struct pool_workqueue *pwq;	4095	struct pool_workqueue *pwq;
4087		4096
		4097	/* see the comment above the definition of WQ_POWER_EFFICIENT */
		4098	if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient)
		4099	flags \|= WQ_UNBOUND;
		4100
4088	/* allocate wq and format name */	4101	/* allocate wq and format name */
4089	if (flags & WQ_UNBOUND)	4102	if (flags & WQ_UNBOUND)
4090	tbl_size = wq_numa_tbl_len * sizeof(wq->numa_pwq_tbl[0]);	4103	tbl_size = wq_numa_tbl_len * sizeof(wq->numa_pwq_tbl[0]);