linux-kernel - Re: [PATCH] pm_qos: Add system bus performance parameter

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Date:	Thu, 26 Aug 2010 23:41:54 -0700
From:	mark gross <markgross@...gnar.org>
To:	Saravana Kannan <skannan@...eaurora.org>
Cc:	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	James Bottomley <James.Bottomley@...e.de>,
	mark gross <markgross@...gnar.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jonathan Corbet <corbet@....net>, khilman@...prootsystems.com
Subject: Re: [PATCH] pm_qos: Add system bus performance parameter

On Thu, Aug 26, 2010 at 09:13:23PM -0700, Saravana Kannan wrote:
> 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@...eaurora.org>
> ---
>  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,
> -- 
> 1.7.1.1
> ---

nack.

Change the name to system_bus_throughput_pm_qos assuming KBS units and
I'll ok it.  It needs to be portable and without units I think drivers
will start using magic numbers that will break when you go from a
devices with 16 to 32 bus with the same clock.

We had an email thread about this last year 
http://lkml.org/lkml/2009/12/31/143
I don't recall solution ever coming out of it.   I think you guys didn't
like the idea of using units.  Further I did post a patch adding
something like using units. Although I looks like I botch the post the
linux-pm as I can't seem to find it in the linux-pm archives :(
http://lkml.org/lkml/2010/4/22/213

Would you be ok with using throughput instead of a unit less performance
magic number?


--mark


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