Hello, Please forgive the delay in commenting - I am just now catching up on these huge E-mail threads; On Mon, 3 May 2010, Alan Stern wrote: > So for example, runtime PM cannot be used to put the system into an S3 > sleep state. This is not quite true. Runtime PM, *in conjunction with CPUIdle,* can put many current embedded Linux systems into not just S3, but actually S5. This is done right now on OMAP in mainline Linux[1]. (S5 is called "C6" in that codebase, since the CPUIdle governor is used - this is a misnomer.) This approach allows the system to wake up, or stay running, as requested by the timer subsystem, or the scheduler. No suspend-block-like API is needed. Several consumer-market Linux devices have already shipped using this mechanism. > The simplest example is that suspend blockers can be used to control > whether or not the CPU shuts down, whereas runtime PM can't. Runtime PM still needs to be combined with some sort of governor to control not only CPU power states, but also system power states. CPUIdle works pretty well as a system power governor for a single-CPU system, but is admittedly something of a hack[2]. Going forward, some sort of basic, system-wide governor is a cleaner design[3]. But since the "opportunistic suspend" governor proposed in patch 1 ignores timer expiries and the scheduler runqueue, and then hacks around that decision by inserting suspend-block calls into code that would otherwise work normally, it's not a good approach. - Paul 1. http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=arch/arm/mach-omap2/cpuidle34xx.c;h=3d3d035db9aff62ce522e0080e570cfdbf8e70cc;hb=4462dc02842698f173f518c1f5ce79c0fb89395a#l292 2. Paul Walmsley E-mail to the linux-pm mailing list, dated Thu, 13 May 2010 13:01:33 -0600: http://permalink.gmane.org/gmane.linux.power-management.general/18592 3. ibid. _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
