[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [Xen-devel] cpu_down() but no cpu_up() in drivers/xen/cpu_hotplug.c ?
>-----Original Message----- >From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx >[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Jeremy Fitzhardinge >Sent: Wednesday, May 12, 2010 1:40 AM >To: Ian Campbell >Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; Jan Beulich >Subject: Re: [Xen-devel] cpu_down() but no cpu_up() in >drivers/xen/cpu_hotplug.c ? > >On 05/11/2010 02:45 AM, Ian Campbell wrote: >> The original commit which added CPU hotplug to pvops says: >> >> xen: implement CPU hotplugging >> >> Note the changes from 2.6.18-xen CPU hotplugging: >> >> A vcpu_down request from the remote admin via Xenbus both hotunplugs the >> CPU, and disables it by removing it from the cpu_present map, and >> removing >> its entry in /sys. >> >> A vcpu_up request from the remote admin only re-enables the CPU, and does >> not immediately bring the CPU up. A udev event is emitted, which can be >> caught by the user if he wishes to automatically re-up CPUs when >> available, >> or implement a more complex policy. >> >> Signed-off-by: Alex Nixon <alex.nixon@xxxxxxxxxx> >> Acked-by: Jeremy Fitzhardinge <jeremy@xxxxxxxx> >> Signed-off-by: Ingo Molnar <mingo@xxxxxxx> >> >> I'm not sure how the decision was reached to implement it this way, >> perhaps for consistency with CPU hotplug on other >> platforms/architectures? >> > >Yes, it was to make it consistent with native physical CPU hotplug. It >also replaced some other xen-specific mechanism to allow the domain to >control when the cpu was actually added (I forget the details; something >like "cpus allowed" vs "cpus active" or something?). I remember for cpu remove, the xen's vcpu is different to native method. In native, it will only trigger a uevent to user space (at least in version like 2.6.31), while for xen vcpu, it will remove the vcpu directly. --jyh > >> FWIW I use a udev rule to bring up CPUs as they are added, which is >> equivalent to the old behaviour: >> >> ACTION=="add", SUBSYSTEM=="cpu", RUN+="/bin/sh -c '[ ! -e >/sys$devpath/online ] || echo 1 > /sys$devpath/online'" >> > >Fedora and RHEL have been shipping with something like this for a while. > > J > >_______________________________________________ >Xen-devel mailing list >Xen-devel@xxxxxxxxxxxxxxxxxxx >http://lists.xensource.com/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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