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

[Amit Kucheria]

On Thu, Apr 25, 2013 at 9:13 AM, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> 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>

For the series, you can add my:

Reviewed-by: Amit Kucheria <amit.kucheria@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]);
--
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