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Date: Sat, 23 May 2009 08:07:55 -0700 From: "Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com> To: Peter Zijlstra <a.p.zijlstra@...llo.nl> CC: "mingo@...e.hu" <mingo@...e.hu>, "tglx@...utronix.de" <tglx@...utronix.de>, "hpa@...or.com" <hpa@...or.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "lenb@...nel.org" <lenb@...nel.org>, "Li, Shaohua" <shaohua.li@...el.com>, "svaidy@...ux.vnet.ibm.com" <svaidy@...ux.vnet.ibm.com> Subject: RE: [patch 1/2] x86: Add pm_play_dead funcptr to power-efficiently offline CPUs >-----Original Message----- >From: Peter Zijlstra [mailto:a.p.zijlstra@...llo.nl] >Sent: Saturday, May 23, 2009 3:45 AM >To: Pallipadi, Venkatesh >Cc: mingo@...e.hu; tglx@...utronix.de; hpa@...or.com; >linux-kernel@...r.kernel.org; lenb@...nel.org; Li, Shaohua; >svaidy@...ux.vnet.ibm.com >Subject: Re: [patch 1/2] x86: Add pm_play_dead funcptr to >power-efficiently offline CPUs > >On Fri, 2009-05-22 at 16:19 -0700, venkatesh.pallipadi@...el.com wrote: >> plain text document attachment >> (0001-x86-Add-pm_play_dead-funcptr-to-power-efficiently-o.patch) >> Add a funcptr pm_play_dead (similar to pm_idle) that can take >> the offline CPUs to the most power efficient idle state. >> >> This patch just adds the func pointer. The pointer will get >initialized >> by patch that follows. > >Since the pm_idle function pointer has given us so much grief, I don't >think its wise to repeat that particular disaster. > >I'd much rather see a framework where idle functions can be registered, >and selected from based on criteria such as wakeup latency as provided >by the pm_qos stuff, and power saving. > >This framework should be shared between hotplug-idle and the regular >idle routines. Hotplug would of course not care about things >like wakeup >latency and might therefore pick another idle routine. > Yes. Thought about that approach. There are issues with that approach however. - It would be ugly as we have to add logic in various low level idle handlers we have today mwait_idle, default_idle, acpi_mwait_idle, acpi_ioport_idle to make them aware of offline idle case and disable interrupt and not enable interrupt while going idle and not to wake up on interrupt. - There are limitations on what we can and cannot do when offline. We have had issues with calling acpi methods and/or IO port accesses, during suspend before, so CPU going on suspend only uses C1. Specifically, with the above approach we will have: 1) CPU 1 going offline and starts using regular ACPI IO port C-states. 2) CPU 0 starts suspend and after some points it is unsafe to access ACPI io port accesses, which can potentially result in crash/hangs. So, I would like to keep ACPI out of play_dead. And keeping idle and play_dead separate seemed to be cleaner way to do it. Thanks, Venki -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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