2011/12/21 Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>: > On Wed, Dec 21, 2011 at 05:23:48PM +0800, Barry Song wrote: >> Hi guys, >> i tried cpuhotplug on pandaboard for both >> Pandroid_Froyo_L27.8.2_release_pkg and Linaro 11.11. It has failed to >> work stably. >> On Pandroid_Froyo_L27.8.2_release_pkg, unplugging cpu1 works well: >> # echo 0 > /sys/devices/system/cpu/cpu1/online >> CPU1: shutdown >> >> if i enable the cpu1 again by "echo 1 > >> /sys/devices/system/cpu/cpu1/online", the system will restore to 3 >> random status: hang, normal, panic. >> >> Using Linaro 11.11 release, "echo 0 > >> /sys/devices/system/cpu/cpu1/online" will make system hang and the >> whole system will not be able to reset by pressing reset key, the only >> way to reset system is pulling out AV power. >> >> i am sorry i can't get more time to debug and find more clues. just >> want to ask people whether this is a version the cpuhotplug works >> normal on? > > cpu hotplug is basically totally buggered - the preconditions placed > upon the bringup code path are basically impossible to satisfy in any > shape or form at the moment. > > There's the requirement that the secondary CPU is marked online and > active before interrupts are enabled for the thread migration stuff > to behave correctly. However, this is incompatible with smp_call_function() > which will wait for online CPUs to respond to an IPI - which this one > won't because interrupts are disabled. > > I think there was some discussion about how to fix this but I don't > recall the details. thanks, Russell. then could i think this is an ARM-kernel-specific bug which exists on all ARM SMP chips for the moment? and that bug doesn't happen on x86: root@ubuntu:~/simple-rootfs/initrd/bin# echo 0 > /sys/devices/system/cpu/cpu3/online root@ubuntu:~/simple-rootfs/initrd/bin# echo 1 > /sys/devices/system/cpu/cpu3/online root@ubuntu:~/simple-rootfs/initrd/bin# echo 0 > /sys/devices/system/cpu/cpu2/online root@ubuntu:~/simple-rootfs/initrd/bin# echo 1 > /sys/devices/system/cpu/cpu2/online -barry -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
