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workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues

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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.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Viresh Kumar
2013-04-08 16:45:40 +05:30
committed by Tejun Heo
parent f722406faa
commit cee22a1505
4 changed files with 75 additions and 0 deletions
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15
Documentation/kernel-parameters.txt
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@@ -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.