> ----- Original Message ----- > From: "Paolo Bonzini" <pbonzini@xxxxxxxxxx> > To: "Andrew Jones" <drjones@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, kvm@xxxxxxxxxxxxxxx > Cc: uobergfe@xxxxxxxxxx, dzickus@xxxxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx, mingo@xxxxxxxxxx > Sent: Thursday, July 24, 2014 12:46:11 PM > Subject: Re: [PATCH 2/3] watchdog: control hard lockup detection default > >Il 24/07/2014 12:13, Andrew Jones 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. Regards, Uli -- 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
