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Message-ID: <87zk1967jn.fsf@nemi.mork.no> Date: Wed, 19 Dec 2012 22:44:44 +0100 From: Bjørn Mork <bjorn@...k.no> To: Don Zickus <dzickus@...hat.com> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, Norbert Warmuth <nwarmuth@...nline.de>, Joseph Salisbury <joseph.salisbury@...onical.com>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [RESEND][PATCH v3] watchdog: Fix disable/enable regression Bjørn Mork <bjorn@...k.no> writes: > Don Zickus <dzickus@...hat.com> writes: > >> What about the opposite cases? >> nmi_watchdog=1 >> echo 1 > /sys/devices/system/cpu/cpu1/online > > I don't see why not. But verifying it would be nice. I thought that it > would be a simple thing to test using qemu-kvm, but it seems that the > CPU hotplugging support there isn't quite ready. The guest just dies > with "Assertion `bus->allow_hotplug' failed." > > I'll go digging for alternatives, but if anyone else could verify this > then I'd appreciate it. I just realized that you might not really want/need hotplugging, but just booting with some cores initially offline? That's easier to test at least: qmitest:~# cat /proc/cmdline initrd=/initrd.img.test root=/dev/sda1 ro console=tty0 console=ttyS0,9600n8 maxcpus=1 BOOT_IMAGE=/vmlinuz.test qmitest:~# grep . /sys/devices/system/cpu/o*line /sys/devices/system/cpu/offline:1-3 /sys/devices/system/cpu/online:0 qmitest:~# grep . /sys/devices/system/cpu/cpu?/online /sys/devices/system/cpu/cpu1/online:0 /sys/devices/system/cpu/cpu2/online:0 /sys/devices/system/cpu/cpu3/online:0 qmitest:~# grep . /sys/devices/system/cpu/o*line /sys/devices/system/cpu/offline:1-3 /sys/devices/system/cpu/online:0 qmitest:~# grep . /proc/sys/kernel/nmi_watchdog 1 qmitest:~# echo 1 > /sys/devices/system/cpu/cpu1/online qmitest:~# echo 1 > /sys/devices/system/cpu/cpu2/online qmitest:~# grep . /sys/devices/system/cpu/cpu?/online /sys/devices/system/cpu/cpu1/online:1 /sys/devices/system/cpu/cpu2/online:1 /sys/devices/system/cpu/cpu3/online:0 No problem observed. As expected. Bjørn -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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