linux-kernel - Re: [linux-pm] [PATCH 1/8] PM: Add suspend block api.

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Date:	Tue, 4 May 2010 09:59:59 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	markgross@...gnar.org
cc:	Arve Hjønnevåg <arve@...roid.com>,
	Len Brown <len.brown@...el.com>, <linux-doc@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	<linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
	Magnus Damm <damm@...l.co.jp>,
	<linux-pm@...ts.linux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [linux-pm] [PATCH 1/8] PM: Add suspend block api.

On Mon, 3 May 2010, mark gross wrote:

> You know things would be so much easier if the policy was a one-shot
> styled thing.  i.e. when enabled it does what it does, but upon resume
> the policy must be re-enabled by user mode to get the opportunistic
> behavior.  That way we don't need to grab the suspend blocker from the
> wake up irq handler all the way up to user mode as the example below
> calls out.  I suppose doing this would put a burden on the user mode code
> to keep track of if it has no pending blockers registered after a wake
> up from the suspend.  but that seems nicer to me than sprinkling
> overlapping blocker critical sections from the mettle up to user mode.
> 
> Please consider making the policy a one shot API that needs to be
> re-enabled after resume by user mode.  That would remove my issue with
> the design.

This won't work right if a second IRQ arrives while the first is being
processed.  Suppose the kernel driver for the second IRQ doesn't
activate a suspend blocker, and suppose all the userspace handlers for
the first IRQ end (and the opportunistic policy is re-enabled) before
the userspace handler for the second IRQ can start.  Then the system
will go back to sleep before userspace can handle the second IRQ.

Alan Stern

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