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

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Date:	Tue, 19 Aug 2014 09:20:20 +0200
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	Pavel Machek <pavel@....cz>
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

On 16 August 2014 08:35, Pavel Machek <pavel@....cz> wrote:
>>
>> @@ -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.

Yeah, I was a bit concerned about excessive rounding increasing the
chances of going to a higher frequency step than strictly necessary,
but after thinking a bit more about it, I think it won't be a problem
because it would be a bad idea anyway to only take into account
explicit bandwidth requirements when calculating the optimal memory
bus frequency.

So I agree that a coarser unit such as mbps should be more appropriate here.

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

Will do.

> Otherwise looks good,
>
> Acked-by: Pavel Machek <pavel@....cz>

Thanks,

Tomeu

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