Commit cf454aec authored Feb 12, 2010 by Don Zickus Committed by Ingo Molnar Feb 14, 2010

nmi_watchdog: Fallback to software events when no hardware pmu detected



Not all arches have a PMU or have perf_event support for their
PMU.  The nmi_watchdog will fail in those cases.  Fallback to
using software events to generate nmi_watchdog traffic with
local apic interrupts.

Tested on a Pentium4 and it worked as expected, excepting for
detecting cpu lockups.

The problem with using software events as a cpu lock up detector
is the nmi_watchdog uses the logic that if local apic interrupts
stop incrementing then the cpu is probably locked up.  But with
software events we use the local apic to trigger the
nmi_watchdog callback to see if local apic interrupts are still
firing, which obviously they are otherwise we wouldn't have been
triggered.

The algorithm to detect cpu lock ups is the same as the old
nmi_watchdog. Perhaps we need to find a better way to detect
lock ups?

Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: peterz@infradead.org
Cc: gorcunov@gmail.com
Cc: aris@redhat.com
LKML-Reference: <1266013161-31197-3-git-send-email-dzickus@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 504d7cf1

kernel/nmi_watchdog.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -165,10 +165,14 @@ cpu_callback(struct notifier_block nfb, unsigned long action, void hcpu)
		/* originally wanted the below chunk to be in CPU_UP_PREPARE, but caps is unpriv for non-CPU0 */
		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)) {
		wd_attr.type = PERF_TYPE_SOFTWARE;
		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;
		}
		}
		per_cpu(nmi_watchdog_ev, hotcpu) = event;
		perf_event_enable(per_cpu(nmi_watchdog_ev, hotcpu));
		break;

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