linux-kernel - Re: [RFC v2 1/3] PM / QoS: Add PM_QOS_MEMORY

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Date:	Sat, 16 Aug 2014 08:35:17 +0200
From:	Pavel Machek <pavel@....cz>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:	linux-pm@...r.kernel.org,
	Thierry Reding <thierry.reding@...il.com>,
	Terje Bergstr?m <tbergstrom@...dia.com>,
	Stephen Warren <swarren@...dotorg.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Mikko Perttunen <mperttunen@...dia.com>
Subject: Re: [RFC v2 1/3] PM / QoS: Add PM_QOS_MEMORY_BANDWIDTH class

Hi!

> Also adds a class type PM_QOS_SUM that aggregates the values by summing them.
> 
> It can be used by memory controllers to calculate the optimum clock frequency
> based on the bandwidth needs of the different memory clients.
> 
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
> ---
>  Documentation/power/pm_qos_interface.txt |  4 +++-
>  include/linux/pm_qos.h                   |  5 ++++-
>  kernel/power/qos.c                       | 27 ++++++++++++++++++++++++++-
>  3 files changed, 33 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/power/pm_qos_interface.txt b/Documentation/power/pm_qos_interface.txt
> index a5da5c7..57782e8 100644
> --- a/Documentation/power/pm_qos_interface.txt
> +++ b/Documentation/power/pm_qos_interface.txt
> @@ -5,7 +5,8 @@ performance expectations by drivers, subsystems and user space applications on
>  one of the parameters.
>  
>  Two different PM QoS frameworks are available:
> -1. PM QoS classes for cpu_dma_latency, network_latency, network_throughput.
> +1. PM QoS classes for cpu_dma_latency, network_latency, network_throughput,
> +memory_bandwidth.
>  2. the per-device PM QoS framework provides the API to manage the per-device latency
>  constraints and PM QoS flags.
>  
> @@ -13,6 +14,7 @@ Each parameters have defined units:
>   * latency: usec
>   * timeout: usec
>   * throughput: kbs (kilo bit / sec)
> + * memory bandwidth: kbs (kilo bit / sec)

Would mega bits per second make sense here?

I suppose some many-core systems would have memory bandwith
in > 10 terabit/sec, overflowing u32.

Plus, if driver in 3/3 is just an example, perhaps comment
should explain that clearly?

Otherwise looks good,

Acked-by: Pavel Machek <pavel@....cz>
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