Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

mark gross
2010-05-29T03:10:38Z

On Thu, May 27, 2010 at 11:06:23AM -0400, Alan Stern wrote:
> If people don't mind, here is a greatly simplified summary of the
> comments and objections I have seen so far on this thread:
>
> The in-kernel suspend blocker implementation is okay, even
> beneficial.

Only if they only block. You get into trouble when the in kernel
un-block opperation triggers an implicit suspend.

>
> Opportunistic suspends are okay.
>
> The proposed userspace API is too Android-specific.
>
> More kernel mechanisms are needed for expressing processes'
> latency requirements.

True.

--mgross

>
> The last one is obviously a longer-term issue, so let's ignore it for
> now. That leaves as the only point of contention the userspace
> suspend-blocker API.
>
> The proposal I made a couple of days ago removes this API and leaves
> the other things (i.e., the in-kernel suspend blockers and
> opportunistic suspend) intact. In place of the userspace
> kernel-blocker API, Android would have to implement a power manager
> process that would essentially juggle all the latency requirements in
> userspace.
>
> Communication between the power manager process and the kernel would be
> limited to adding a new "opportunistic" entry to /sys/power/state --
> something which could well be useful in its own right. Even if this
> API turns out not to be good, it's simple enough that it could be
> removed pretty easily.
>
> This answers Alan Cox's (and other's) desire not to implement a
> questionable or special-purpose API. And it also answers Thomas's
> desire to make scheduling decisions based on latency requirements
> (although the answer is simply to punt all these decisions out of the
> kernel and into userspace -- which is reasonable for now since the
> alternative would require a long-term kernel development effort).
>
> Indeed, having a power manager thread may well turn out to be a useful
> thing -- but even if it doesn't, this scheme minimizes the damage while
> still allowing the Android platform to use a vanilla kernel with only
> limited modifications to their userspace.
>
> Alan Stern
>
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