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SubjectRe: [PATCH] pm_qos: Add system bus performance parameter
Date
Saravana Kannan <skannan@codeaurora.org> writes:

> Some drivers/devices might need some minimum system bus performance to
> provide acceptable service. Provide a PM QoS parameter to send these requests
> to.
>
> The new parameter is named "system bus performance" since it is generic enough
> for the unit of the request to be frequency, bandwidth or something else that
> might be appropriate. It's up to each implementation of the QoS provider to
> define what the unit of the request would be.
>
> Signed-off-by: Saravana Kannan <skannan@codeaurora.org>

With this current design, only one system-wide bus would be managed.
What if a platform has more than one independently scalable bus?

I think the only scalable way to handle this kind of thing is to have
per-device QoS constraints that can then be combined/aggregated by parent
devices/busses.

At LPC this year, I've proposed per-device QoS constraints[1] as a topic
for the PM mini-conf. I hope some folks from the MSM camp can be there
for these discussions.

Kevin

[1] http://www.linuxplumbersconf.org/2010/ocw/proposals/819

> ---
> kernel/pm_qos_params.c | 9 +++++++++
> 1 files changed, 9 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/pm_qos_params.c b/kernel/pm_qos_params.c
> index 996a4de..1a44a67 100644
> --- a/kernel/pm_qos_params.c
> +++ b/kernel/pm_qos_params.c
> @@ -93,12 +93,21 @@ static struct pm_qos_object network_throughput_pm_qos = {
> .type = PM_QOS_MAX,
> };
>
> +static BLOCKING_NOTIFIER_HEAD(system_bus_performance_notifier);
> +static struct pm_qos_object system_bus_performance_pm_qos = {
> + .requests = PLIST_HEAD_INIT(system_bus_performance_pm_qos.requests, pm_qos_lock),
> + .notifiers = &system_bus_performance_notifier,
> + .name = "system_bus_performance",
> + .default_value = 0,
> + .type = PM_QOS_MAX,
> +};
>
> static struct pm_qos_object *pm_qos_array[] = {
> &null_pm_qos,
> &cpu_dma_pm_qos,
> &network_lat_pm_qos,
> &network_throughput_pm_qos
> + &system_bus_performance_pm_qos
> };
>
> static ssize_t pm_qos_power_write(struct file *filp, const char __user *buf,


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