linux-kernel - Re: pm qos infrastructure and interface

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Message-ID: <20071011150804.GA7293@linux.intel.com>
Date:	Thu, 11 Oct 2007 08:08:04 -0700
From:	Mark Gross <mgross@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	arjan@...radead.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, linux-pm@...ts.linux-foundation.org,
	mark.gross@...el.com
Subject: Re: pm qos infrastructure and interface

On Wed, Oct 10, 2007 at 10:17:04PM -0700, Andrew Morton wrote:
> On Thu, 4 Oct 2007 14:51:39 -0700 Mark Gross <mgross@...ux.intel.com> wrote:
> 
> > The following patch is a generalization of the latency.c implementation
> > done by Arjan last year.  It provides infrastructure for more than one
> > parameter, and exposes a user mode interface for processes to register
> > pm_qos expectations of processes.
> > 
> > 
> > This interface provides a kernel and user mode interface for registering
> > performance expectations by drivers, subsystems and user space
> > applications on one of the parameters.
> > 
> > Currently we have {cpu_dma_latency, network_latency, network_throughput}
> > as the initial set of pm_qos parameters.
> > 
> > The infrastructure exposes multiple misc device nodes one per
> > implemented parameter.  The set of parameters implement is defined by
> > pm_qos_power_init() and pm_qos_params.h.  This is done because having
> > the available parameters being runtime configurable or changeable from a
> > driver was seen as too easy to abuse.
> 
> I'm a bit surprised that this change appears to have no configurability.
> If one has set CONFIG_PM=n (for example), shouldn't it all go away?

We considered that as an option but as latency.c didn't offer it I
didn't either.  

I could see the user mode interface portion of the implementation be
made as a compile time option but the kernel infrastructure will
continue to be needed by at least cpu-idel, pcm_native.c and ipw2100.

You know it could make sense to have the user mode interface part of the
patch as configurable or a build time dependent of sysfs and misc device
support for the linux-tiny guys.  Is it practical to make a linux-tiny
without the sysfs infrastructure needed to make a misc device?  I'll ask
on the linux-tiny list.

--mgross
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