Messages in this thread | | | From | Song Liu <> | Subject | Re: [PATCH v4] watchdog: Allow nmi watchdog to use "ref-cycles" event | Date | Thu, 18 May 2023 20:12:27 +0000 |
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> On May 17, 2023, at 11:44 PM, Yonghong Song <yhs@meta.com> wrote: > > > > 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?
In most case, all we need is to add "nmi_watchdog=refcycles" to kernel args.
> >> 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.
In that case, we can probably rename the function as hardlockup_use_ref_cycles(). I am fine with either way.
Thanks, Song
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