Commit 393fb313 authored by Song Liu's avatar Song Liu Committed by Andrew Morton
Browse files

watchdog: allow nmi watchdog to use raw perf event 

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=rNNN to configure the watchdog
to use raw event.  For example, on Intel CPUs, we can use "r300" to
configure the watchdog to use ref-cycles event.

If the raw event does not work, fall back to use "cycles".

[akpm@linux-foundation.org: fix kerneldoc]
Link: https://lkml.kernel.org/r/20240430060236.1878002-2-song@kernel.org


Signed-off-by: default avatarSong Liu <song@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 602ba773

Documentation/admin-guide/kernel-parameters.txt

+3 −2
Original line number Diff line number Diff line
@@ -3773,10 +3773,12 @@ 
			Format: [state][,regs][,debounce][,die]



	nmi_watchdog=	[KNL,BUGS=X86] Debugging features for SMP kernels

			Format: [panic,][nopanic,][num]

			Format: [panic,][nopanic,][rNNN,][num]

			Valid num: 0 or 1

			0 - turn hardlockup detector in nmi_watchdog off

			1 - turn hardlockup detector in nmi_watchdog on

			rNNN - configure the watchdog with raw perf event 0xNNN



			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)
@@ -7464,4 +7466,3 @@ 
				memory, and other data can't be written using

				xmon commands.

			off	xmon is disabled.

include/linux/nmi.h

+2 −0
Original line number Diff line number Diff line
@@ -105,10 +105,12 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs); 
extern void hardlockup_detector_perf_stop(void);

extern void hardlockup_detector_perf_restart(void);

extern void hardlockup_detector_perf_cleanup(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_cleanup(void) { }

static inline void hardlockup_config_perf_event(const char *str) { }

#endif



void watchdog_hardlockup_stop(void);

kernel/watchdog.c

+2 −0
Original line number Diff line number Diff line
@@ -80,6 +80,8 @@ static int __init hardlockup_panic_setup(char *str) 
		watchdog_hardlockup_user_enabled = 0;

	else if (!strncmp(str, "1", 1))

		watchdog_hardlockup_user_enabled = 1;

	else if (!strncmp(str, "r", 1))

		hardlockup_config_perf_event(str + 1);

	while (*(str++)) {

		if (*str == ',') {

			str++;

kernel/watchdog_perf.c

+46 −0
Original line number Diff line number Diff line
@@ -90,6 +90,14 @@ static struct perf_event_attr wd_hw_attr = { 
	.disabled	= 1,

};



static struct perf_event_attr fallback_wd_hw_attr = {

	.type		= PERF_TYPE_HARDWARE,

	.config		= PERF_COUNT_HW_CPU_CYCLES,

	.size		= sizeof(struct perf_event_attr),

	.pinned		= 1,

	.disabled	= 1,

};



/* Callback function for perf event subsystem */

static void watchdog_overflow_callback(struct perf_event *event,

				       struct perf_sample_data *data,
@@ -122,6 +130,13 @@ static int hardlockup_detector_event_create(void) 
	/* Try to register using hardware perf events */

	evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,

					       watchdog_overflow_callback, NULL);

	if (IS_ERR(evt)) {

		wd_attr = &fallback_wd_hw_attr;

		wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);

		evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,

						       watchdog_overflow_callback, NULL);

	}



	if (IS_ERR(evt)) {

		pr_debug("Perf event create on CPU %d failed with %ld\n", cpu,

			 PTR_ERR(evt));
@@ -259,3 +274,34 @@ int __init watchdog_hardlockup_probe(void) 
	}

	return ret;

}



/**

 * hardlockup_config_perf_event - Overwrite config of wd_hw_attr.

 *

 * @str: number which identifies the raw perf event to use

 */

void __init hardlockup_config_perf_event(const char *str)

{

	u64 config;

	char buf[24];

	char *comma = strchr(str, ',');



	if (!comma) {

		if (kstrtoull(str, 16, &config))

			return;

	} else {

		unsigned int len = comma - str;



		if (len >= sizeof(buf))

			return;



		if (strscpy(buf, str, sizeof(buf)) < 0)

			return;

		buf[len] = 0;

		if (kstrtoull(buf, 16, &config))

			return;

	}



	wd_hw_attr.type = PERF_TYPE_RAW;

	wd_hw_attr.config = config;

}