Messages in this thread | | | Date | Tue, 06 Dec 2011 19:45:36 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [PATCH v4 0/7] x86: BSP or CPU0 online/offline |
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On 12/06/2011 02:12 PM, Ingo Molnar wrote:
> > * Fenghua Yu <fenghua.yu@intel.com> wrote: > >> From: Fenghua Yu <fenghua.yu@intel.com> >> >> BSP or CPU0 has been the last obstacle to CPU hotplug on x86. >> This patch set implements BSP online and offline and removes >> this obstacle to CPU hotplug.
[snip] >
> Also, could you please enumerate all limitations that could > possibly happen? The documentation has this list right now: > > +1. Resume from hibernate/suspend depends on BSP. Hibernate/suspend will fail if > +BSP is offline and you need to online BSP before hibernate/suspend can continue. > > This needs to be fixed on some other fashion than warning people > in documentation that it would break. >
Actually, this patchset does more than just warn people. It has checks to see if the CPU0 is offline, and if so, it fails the suspend/hibernate attempt. See patch 7/7 (x86/power/cpu.c: Don't hibernate/suspend if CPU0 is offline)
> Firstly, at minimum a suspend/hibernate attempt should fail in > some deterministic fashion.
It does, as mentioned above. In fact, this patchset does it proactively: whether the hardware/firmware supports suspend/resume with BSP offlined or not, it just prevents anybody from doing suspend/hibernate when the boot CPU is offline.
I am not saying that this is the *right* way to do it; I am just pointing out that this patchset _does_ handle it.
> > Secondly, and more importantly, is there *any* hardware in > existence that has a BIOS that can suspend/resume successfully > with BSP offlined? If such hardware exists then we need to > support it properly - initially perhaps by whitelisting such > systems. > > Then if demand for this picks up some more intelligent method of > cooperating with the firmware could be added: the firmware could > actually signal to us whether it supports suspend/resume from > other than the boot CPU. >
Regards, Srivatsa S. Bhat
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