On Thu 2022-03-24 22:14:05, Lecopzer Chen wrote: > With the recent feature added to enable perf events to use pseudo NMIs > as interrupts on platforms which support GICv3 or later, its now been > possible to enable hard lockup detector (or NMI watchdog) on arm64 > platforms. So enable corresponding support. > > One thing to note here is that normally lockup detector is initialized > just after the early initcalls but PMU on arm64 comes up much later as > device_initcall(). To cope with that, overriding watchdog_nmi_probe() to > let the watchdog framework know PMU not ready, and inform the framework > to re-initialize lockup detection once PMU has been initialized. > > [1]: http://lore.kernel.org/linux-arm-kernel/1610712101-14929-1-git-send-email-sumit.garg@xxxxxxxxxx > > --- /dev/null > +++ b/arch/arm64/kernel/watchdog_hld.c > @@ -0,0 +1,37 @@ > +// SPDX-License-Identifier: GPL-2.0 > +#include <linux/nmi.h> > +#include <linux/cpufreq.h> > +#include <linux/perf/arm_pmu.h> > + > +/* > + * Safe maximum CPU frequency in case a particular platform doesn't implement > + * cpufreq driver. Although, architecture doesn't put any restrictions on > + * maximum frequency but 5 GHz seems to be safe maximum given the available > + * Arm CPUs in the market which are clocked much less than 5 GHz. On the other > + * hand, we can't make it much higher as it would lead to a large hard-lockup > + * detection timeout on parts which are running slower (eg. 1GHz on > + * Developerbox) and doesn't possess a cpufreq driver. > + */ > +#define SAFE_MAX_CPU_FREQ 5000000000UL // 5 GHz > +u64 hw_nmi_get_sample_period(int watchdog_thresh) > +{ > + unsigned int cpu = smp_processor_id(); > + unsigned long max_cpu_freq; > + > + max_cpu_freq = cpufreq_get_hw_max_freq(cpu) * 1000UL; > + if (!max_cpu_freq) > + max_cpu_freq = SAFE_MAX_CPU_FREQ; > + > + return (u64)max_cpu_freq * watchdog_thresh; > +} This change is not mentioned in the commit message. Please, put it into a separate patch. > +int __init watchdog_nmi_probe(void) > +{ > + if (!allow_lockup_detector_init_retry) > + return -EBUSY; How do you know that you should return -EBUSY when retry in not enabled? I guess that it is an optimization to make it fast during the first call. But the logic is far from obvious. > + > + if (!arm_pmu_irq_is_nmi()) > + return -ENODEV; > + > + return hardlockup_detector_perf_init(); > +} Is this just an optimization or is it really needed? Why this was not needed in v2 patchset? If it is just an optimization then I would remove it. IMHO, it just adds confusion and it is not worth it. Best Regards, Petr
