Messages in this thread | | | Date | Sat, 3 Jun 2023 00:47:44 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4] watchdog: Allow nmi watchdog to use "ref-cycles" event |
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On Wed, May 17, 2023 at 05:25:55PM -0700, Song Liu wrote: > NMI watchdog permanently consumes one hardware counters per CPU on the > system. For systems that use many hardware counters, this causes more > aggressive time multiplexing of perf events. > > OTOH, some CPUs (mostly Intel) support "ref-cycles" event, which is rarely > used. Add kernel cmdline arg nmi_watchdog=ref-cycles to configure the > watchdog to use "ref-cycles" event instead of "cycles". > > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Signed-off-by: Song Liu <song@kernel.org> > > --- > Changes in v4: > Fix compile error for !CONFIG_HARDLOCKUP_DETECTOR_PERF. (kernel test bot) > > Changes in v3: > > Pivot the design to use kernel arg nmi_watchdog=ref-cycles (Peter) > --- > Documentation/admin-guide/kernel-parameters.txt | 5 +++-- > include/linux/nmi.h | 2 ++ > kernel/watchdog.c | 2 ++ > kernel/watchdog_hld.c | 9 +++++++++ > 4 files changed, 16 insertions(+), 2 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 9e5bab29685f..d378e23dad7c 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -3593,10 +3593,12 @@ > Format: [state][,regs][,debounce][,die] > > nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels > - Format: [panic,][nopanic,][num] > + Format: [panic,][nopanic,][ref-cycles][num] > Valid num: 0 or 1 > 0 - turn hardlockup detector in nmi_watchdog off > 1 - turn hardlockup detector in nmi_watchdog on > + ref-cycles - configure the watchdog with perf event > + "ref-cycles" instead of "cycles" > When panic is specified, panic when an NMI watchdog > timeout occurs (or 'nopanic' to not panic on an NMI > watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
I still hate the whole ref-cycles thing, at the very least powerpc also has HAVE_HARDLOCKUP_DETECTOR_PERF and they don't have ref-cycles, but perhaps them wants to use a different event when the moon is just so...
What again was wrong with the option of specifying a raw event value and falling back to cpu-cycles if that fails?
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