Messages in this thread | | | Date | Mon, 15 Feb 2010 10:38:37 -0500 | From | Don Zickus <> | Subject | Re: [PATCH 3/4] nmi_watchdog: fallback to software events when no hardware pmu detected |
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On Mon, Feb 15, 2010 at 11:33:41AM +1100, Paul Mackerras wrote: > 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.
Hmm, good points, I'll work on that and add it to my next round of changes.
Thanks, Don
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