Il 24/07/2014 13:18, Ulrich Obergfell ha scritto: >>> >> The running kernel still has the ability to enable/disable at any >>> >> time with /proc/sys/kernel/nmi_watchdog us usual. However even >>> >> when the default has been overridden /proc/sys/kernel/nmi_watchdog >>> >> will initially show '1'. To truly turn it on one must disable/enable >>> >> it, i.e. >>> >> echo 0 > /proc/sys/kernel/nmi_watchdog >>> >> echo 1 > /proc/sys/kernel/nmi_watchdog >> > >> > Why is it hard to make this show the right value? :) >> > >> > Paolo > 'echo 1 > /proc/sys/kernel/nmi_watchdog' enables both - hard lockup and > soft lockup detection. watchdog_enable_all_cpus() starts a 'watchdog/N' > thread for each CPU. If the kernel runs on a bare metal system where the > processor does not have a PMU, or when perf_event_create_kernel_counter() > returns failure to watchdog_nmi_enable(), or when the kernel runs as a > guest on a hypervisor that does not emulate a PMU, then the 'watchdog/N' > threads are still active for soft lockup detection. Patch 2/3 essentially > makes watchdog_nmi_enable() behave in the same way as if -ENOENT would > have been returned by perf_event_create_kernel_counter(). This is then > reported via a console message. > > NMI watchdog: disabled (cpu0): hardware events not enabled > > It's hard say what _is_ 'the right value' (because lockup detection is > then enabled 'partially'), regardless of whether patch 2/3 is applied > or not. But this means that it is not possible to re-enable softlockup detection only. I think that should be the effect of echo 0 + echo 1, if hardlockup detection was disabled by either the command line or patch 3. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
