Messages in this thread | | | Date | Mon, 15 Feb 2010 11:33:41 +1100 | From | Paul Mackerras <> | Subject | Re: [PATCH 3/4] nmi_watchdog: fallback to software events when no hardware pmu detected |
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On Fri, Feb 12, 2010 at 05:19:20PM -0500, Don Zickus wrote:
> diff --git a/kernel/nmi_watchdog.c b/kernel/nmi_watchdog.c > index 73c1954..4f23505 100644 > --- a/kernel/nmi_watchdog.c > +++ b/kernel/nmi_watchdog.c > @@ -166,8 +166,12 @@ cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu) > wd_attr.sample_period = hw_nmi_get_sample_period(); > event = perf_event_create_kernel_counter(&wd_attr, hotcpu, -1, wd_overflow); > if (IS_ERR(event)) { > - printk(KERN_ERR "nmi watchdog failed to create perf event on %i: %p\n", hotcpu, event); > - return NOTIFY_BAD; > + wd_attr.type = PERF_TYPE_SOFTWARE; > + event = perf_event_create_kernel_counter(&wd_attr, hotcpu, -1, wd_overflow);
Here you don't explicitly set wd_attr.config or wd_attr.sample_period for the software event. So PERF_COUNT_HW_CPU_CYCLES (which is 0) becomes PERF_COUNT_SW_CPU_CLOCK (also 0). Which is either a happy accident or really really subtle. :) I suggest you either set wd_attr.config or add a comment pointing out that you are using the fact that PERF_COUNT_HW_CPU_CYCLES == PERF_COUNT_SW_CPU_CLOCK.
Also you don't explicitly set wd_attr.sample_period, so it will be whatever hw_nmi_get_sample_period() returned, except now measured in nanoseconds rather than (presumably) cpu clock cycles. Are you aiming for 1 interrupt per second? If so you should set .sample_period to NSEC_PER_SEC.
Paul.
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