Messages in this thread | | | From | Dan Streetman <> | Date | Wed, 29 Oct 2014 17:52:10 -0400 | Subject | Re: [PATCH V2] Driver cpu: update online when cpu_up/down besides sysfs |
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On Wed, Oct 29, 2014 at 5:46 PM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote: > On Monday, October 27, 2014 08:46:08 PM Dan Streetman wrote: >> On Mon, Oct 27, 2014 at 5:38 PM, Rafael J. Wysocki >> <rafael.j.wysocki@intel.com> wrote: >> > On 10/27/2014 3:59 AM, Neil Zhang wrote: >> >> >> >> The current per-cpu offline info won't be updated when we use >> >> any other method besides sysfs to call cpu_up/down. >> >> Thus the cpu/online can't reflect the real online status. >> >> >> >> This patch is going to fix the issue introduced by commit >> >> 0902a9044fa5b7a0456ea4daacec2c2b3189ba8c (Driver core: >> >> Use generic offline/online for CPU offline/online) >> >> >> >> CC: Rafael J. Wysocki <rafael.j.wysocki@intel.com> >> >> Tested-by: Dan Streetman <ddstreet@ieee.org> >> >> Signed-off-by: Neil Zhang <zhangwm@marvell.com> >> > >> > >> > Oh dear, no. >> > >> > Please first tell me what exactly the problem you're seeing is. >> >> For some background, here is my last comment on the first email thread on this: >> https://lkml.org/lkml/2014/10/27/595 >> >> I didn't create this patch, but the problem essentially is that before >> your commit the individual cpu online nodes >> (/sys/devices/system/cpu/cpuN/online) stayed in sync during >> cpu_down/up, because they used the cpu_online_mask; while after the >> commit, they are tracked by the cpu's generic dev->offline flag, which >> isn't updated during cpu_down/up. > > Which is not triggered from sysfs. > >> So now, any place in the kernel >> that brings a cpu up or down must also update the cpu->dev->offline >> flag. > > Not any place. In particular, system suspend-resume doesn't need to > do that, because it takes CPUs offline and then brings them back > online. > > If there's a place in the kernel where CPUs are taken offline and > left in that state, then it needs to be updated.
The only place I know of is ppc's dlpar code, as mentioned below.
Neil, as you crafted the original patch, I assume you know of some other place in the kernel doing cpu_up/down directly, where you're seeing this problem?
> >> My interest in the patch was coincidental because I was seeing >> the same problem when using dlpar operations to hotplug cpus, which >> uses the arch/powerpc/platform/pseries/dlpar.c code; that code brings >> a cpu offline when it's hot-removed (and the cpu online when it's >> hot-added), but it hasn't been changed to also update the cpu's >> dev->offline flag. > > It should be modified to do that. > >> As I said in the previous email to the first thread, the ppc dlpar >> operation might be changed in the future to fully unregister a cpu >> when it's hot-removed, which would remove the entire sysfs cpuN >> directory. Alternately and/or until then, it could be updated to >> simply update the cpu'd dev->offline flag (that's what I originally >> did for my own testing). However, without a central place to update >> the cpu's dev->offline field, like this, or possibly in >> set_cpu_online(), or elsewhere during cpu_down/up, each place in the >> kernel that calls cpu_down() or cpu_up() also needs to update the >> dev->offline flag. It's possible that the ppc dlpar code is the only >> place in the kernel that has this problem; I haven't searched. > > It is quite likely to be the only place like that. > > While I'm not familiar with the code in question, the most straightforward > way to fix the problem would be to replace cpu_down() in there with > device_offline(get_cpu_device(cpu)), but that needs to be called under > device_hotplug_lock.
Ok, will do.
> > -- > I speak only for myself. > Rafael J. Wysocki, Intel Open Source Technology Center.
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