Messages in this thread | | | Date | Sat, 29 Jul 2006 16:40:31 -0500 | From | Nathan Lynch <> | Subject | Re: [PATCH -mm][resend] Disable CPU hotplug during suspend |
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Rafael J. Wysocki wrote: > On Saturday 29 July 2006 00:40, Nathan Lynch wrote: > > > But maybe I'm misunderstanding the motivation for using cpu 0 here. I > > had assumed it was because on i386 (and others?) the BSP can't be > > offlined. Is there some other reason? > > Yes. > > First, the arch-dependent suspend code assumes implicitly that it will be > running on the BSP, so some strange things may happen if it doesn't. > > Second, we have to make sure that this function will always leaves the > same CPU online. It's a bit difficult to explain, but I'll do my best. > Suppose that disable_nonboot_cpus() exits running on CPU1, assuming it's > possible. Then the system memory state saved in the suspend image will > reflect this situation. Now the resume code will almost certainly run on the > BSP (say it's CPU0), but when the system memory is restored from the suspend > image the kernel will think it's running on CPU1. > > In the last patch I send yesterday I made disable_nonboot_cpus() check if the > first present CPU, first_cpu(cpu_present_map), is online, try to bring it up > if not and migrate itself to it before the loop over all online CPUs is run. > > I think that's general enough.
I see, thanks for the explanation.
It doesn't look like SMP swsusp would work reliably on platforms where there's a possibility of the cpu maps in the resume and saved images not matching (e.g. ppc64 logical partitions, where cpu 0 could be removed before suspending). But I guess that's largely a theoretical concern at this time. ;)
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