linux-kernel - Re: [PATCH] pm_qos: Add QoS param, minimum system bus frequency

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Date:	Mon, 04 Jan 2010 14:00:45 -0800
From:	Daniel Walker <dwalker@...eaurora.org>
To:	mgross@...ux.intel.com
Cc:	linux-kernel@...r.kernel.org, davidb@...cinc.com,
	pchidamb@...cinc.com
Subject: Re: [PATCH] pm_qos: Add QoS param, minimum system bus frequency

On Mon, 2010-01-04 at 13:38 -0800, mark gross wrote:
> On Thu, Dec 31, 2009 at 05:20:27PM -0800, Daniel Walker wrote:
> > From: Praveen Chidambaram <pchidamb@...cinc.com>
> > 
> > In some systems, the system bus speed can be varied, usually
> > based on the current CPU frequency.  However, various device
> > drivers and/or applications may need a faster system bus for I/O
> > even though the CPU itself may be idle
> 
> What happened to the discussion around multiple platforms needing
> multiple bus pm_qos_requirements?  
> 
> Is system bus freq too generic? (I'm worried about the name space)
> Is this ok? (I'm asking linux-pm for input here.)
> On X86 would this be analogous to FSB, Memory, or PCI bus frequencies?
> What will happen when there are two buses each wanting a PM_QOS
> parameter?  Is that a likely scenario?

We can always change the naming in the future, but someone could add a
PM_QOS_MEMORY_BUS_FREQ or PM_QOS_PERIPHERAL_BUS_FREQ in addition to this
one.. Since it's all generic code having generic naming seems fine..

> Also, on your platform you have a throttling driver controlling the
> frequency of some bus, that will use this value as a constraint on how
> far it will throttle.  no?  I would be interested in seeing this driver
> sometime.  (I just want to make sure no one bastardizes pm_qos into an
> operating point thing.  I'm not sure I can justify why but I want to
> avoid that.)

When you say "operating point thing" do you mean you don't want the
frequency adjusted at runtime? You want it set once then move on?

Daniel

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