Messages in this thread | | | Date | Wed, 17 May 2023 23:44:39 -0700 | Subject | Re: [PATCH v4] watchdog: Allow nmi watchdog to use "ref-cycles" event | From | Yonghong Song <> |
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On 5/17/23 5:25 PM, 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".
Maybe list some example how this new option will used?
> > 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) > @@ -7097,4 +7099,3 @@ > memory, and other data can't be written using > xmon commands. > off xmon is disabled. > - > diff --git a/include/linux/nmi.h b/include/linux/nmi.h > index 048c0b9aa623..edfd1bcce0f6 100644 > --- a/include/linux/nmi.h > +++ b/include/linux/nmi.h > @@ -102,12 +102,14 @@ extern void hardlockup_detector_perf_disable(void); > extern void hardlockup_detector_perf_enable(void); > extern void hardlockup_detector_perf_cleanup(void); > extern int hardlockup_detector_perf_init(void); > +extern void hardlockup_config_perf_event(const char *str); > #else > static inline void hardlockup_detector_perf_stop(void) { } > static inline void hardlockup_detector_perf_restart(void) { } > static inline void hardlockup_detector_perf_disable(void) { } > static inline void hardlockup_detector_perf_enable(void) { } > static inline void hardlockup_detector_perf_cleanup(void) { } > +static inline void hardlockup_config_perf_event(const char *str) { } > # if !defined(CONFIG_HAVE_NMI_WATCHDOG) > static inline int hardlockup_detector_perf_init(void) { return -ENODEV; } > static inline void arch_touch_nmi_watchdog(void) {} > diff --git a/kernel/watchdog.c b/kernel/watchdog.c > index 8e61f21e7e33..fed4f0be8e1a 100644 > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -81,6 +81,8 @@ static int __init hardlockup_panic_setup(char *str) > nmi_watchdog_user_enabled = 0; > else if (!strncmp(str, "1", 1)) > nmi_watchdog_user_enabled = 1; > + else if (!strncmp(str, "ref-cycles", 10))
str vs. 'ref-cycles' is tested here.
> + hardlockup_config_perf_event(str); > return 1; > } > __setup("nmi_watchdog=", hardlockup_panic_setup); > diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c > index 247bf0b1582c..4deca58ba6ed 100644 > --- a/kernel/watchdog_hld.c > +++ b/kernel/watchdog_hld.c > @@ -294,3 +294,12 @@ int __init hardlockup_detector_perf_init(void) > } > return ret; > } > + > +/** > + * hardlockup_config_perf_event - Overwrite config of wd_hw_attr > + */ > +void __init hardlockup_config_perf_event(const char *str) > +{ > + if (!strncmp(str, "ref-cycles", 10))
It is unnecessarily tested again here.
> + wd_hw_attr.config = PERF_COUNT_HW_REF_CPU_CYCLES; > +}
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