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Message-Id: <af5765d2-ba72-481c-8c7a-6fb09fe44709@picoheart.com>
Date: Fri, 5 Dec 2025 14:53:00 +0800
From: "Yicong Yang" <yang.yicong@...oheart.com>
To: "Yunhui Cui" <cuiyunhui@...edance.com>
Cc: <akpm@...ux-foundation.org>, <alex@...ti.fr>, <anup@...infault.org>,
<aou@...s.berkeley.edu>, <atish.patra@...ux.dev>,
<catalin.marinas@....com>, <dianders@...omium.org>,
<johannes@...solutions.net>, <lihuafei1@...wei.com>,
<mark.rutland@....com>, <masahiroy@...nel.org>, <maz@...nel.org>,
<mingo@...nel.org>, <nicolas.schier@...ux.dev>, <palmer@...belt.com>,
<paul.walmsley@...ive.com>, <suzuki.poulose@....com>,
<thorsten.blum@...ux.dev>, <wangjinchao600@...il.com>, <will@...nel.org>,
<yangyicong@...ilicon.com>, <zhanjie9@...ilicon.com>,
<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
<linux-perf-users@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
<yang.yicong@...oheart.com>, <geshijian@...oheart.com>
Subject: Re: [PATCH v6 1/2] watchdog: move arm64 watchdog_hld into common code
On 2025/11/14 11:32, Yunhui Cui wrote:
> Move the contents of arch/arm64/watchdog_hld.c to kernel/watchdog_perf.c
> to create a generic implementation that can be reused by other arch,
> such as RISC-V.
>
> Signed-off-by: Yunhui Cui <cuiyunhui@...edance.com>
> Reviewed-by: Douglas Anderson <dianders@...omium.org>
> ---
> arch/arm64/Kconfig | 1 +
> arch/arm64/kernel/Makefile | 1 -
> arch/arm64/kernel/watchdog_hld.c | 94 --------------------------------
> drivers/perf/arm_pmu.c | 10 +++-
> include/linux/perf/arm_pmu.h | 2 -
> kernel/watchdog_perf.c | 83 ++++++++++++++++++++++++++++
> lib/Kconfig.debug | 8 +++
> 7 files changed, 101 insertions(+), 98 deletions(-)
> delete mode 100644 arch/arm64/kernel/watchdog_hld.c
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 6663ffd23f252..6614ff45b1e06 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -231,6 +231,7 @@ config ARM64
> select HAVE_GCC_PLUGINS
> select HAVE_HARDLOCKUP_DETECTOR_PERF if PERF_EVENTS && \
> HW_PERF_EVENTS && HAVE_PERF_EVENTS_NMI
> + select WATCHDOG_PERF_ADJUST_PERIOD if HARDLOCKUP_DETECTOR_PERF
> select HAVE_HW_BREAKPOINT if PERF_EVENTS
> select HAVE_IOREMAP_PROT
> select HAVE_IRQ_TIME_ACCOUNTING
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index 76f32e424065e..12d77f373fea4 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -44,7 +44,6 @@ obj-$(CONFIG_KUSER_HELPERS) += kuser32.o
> obj-$(CONFIG_FUNCTION_TRACER) += ftrace.o entry-ftrace.o
> obj-$(CONFIG_MODULES) += module.o module-plts.o
> obj-$(CONFIG_PERF_EVENTS) += perf_regs.o perf_callchain.o
> -obj-$(CONFIG_HARDLOCKUP_DETECTOR_PERF) += watchdog_hld.o
> obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
> obj-$(CONFIG_CPU_PM) += sleep.o suspend.o
> obj-$(CONFIG_KGDB) += kgdb.o
> diff --git a/arch/arm64/kernel/watchdog_hld.c b/arch/arm64/kernel/watchdog_hld.c
> deleted file mode 100644
> index 3093037dcb7be..0000000000000
> --- a/arch/arm64/kernel/watchdog_hld.c
> +++ /dev/null
> @@ -1,94 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0
> -#include <linux/nmi.h>
> -#include <linux/cpufreq.h>
> -#include <linux/perf/arm_pmu.h>
> -
> -/*
> - * Safe maximum CPU frequency in case a particular platform doesn't implement
> - * cpufreq driver. Although, architecture doesn't put any restrictions on
> - * maximum frequency but 5 GHz seems to be safe maximum given the available
> - * Arm CPUs in the market which are clocked much less than 5 GHz. On the other
> - * hand, we can't make it much higher as it would lead to a large hard-lockup
> - * detection timeout on parts which are running slower (eg. 1GHz on
> - * Developerbox) and doesn't possess a cpufreq driver.
> - */
> -#define SAFE_MAX_CPU_FREQ 5000000000UL // 5 GHz
> -u64 hw_nmi_get_sample_period(int watchdog_thresh)
> -{
> - unsigned int cpu = smp_processor_id();
> - unsigned long max_cpu_freq;
> -
> - max_cpu_freq = cpufreq_get_hw_max_freq(cpu) * 1000UL;
> - if (!max_cpu_freq)
> - max_cpu_freq = SAFE_MAX_CPU_FREQ;
> -
> - return (u64)max_cpu_freq * watchdog_thresh;
> -}
> -
> -bool __init arch_perf_nmi_is_available(void)
> -{
> - /*
> - * hardlockup_detector_perf_init() will success even if Pseudo-NMI turns off,
> - * however, the pmu interrupts will act like a normal interrupt instead of
> - * NMI and the hardlockup detector would be broken.
> - */
> - return arm_pmu_irq_is_nmi();
> -}
> -
> -static int watchdog_perf_update_period(void *data)
> -{
> - int cpu = smp_processor_id();
> - u64 max_cpu_freq, new_period;
> -
> - max_cpu_freq = cpufreq_get_hw_max_freq(cpu) * 1000UL;
> - if (!max_cpu_freq)
> - return 0;
> -
> - new_period = watchdog_thresh * max_cpu_freq;
> - hardlockup_detector_perf_adjust_period(new_period);
> -
> - return 0;
> -}
> -
> -static int watchdog_freq_notifier_callback(struct notifier_block *nb,
> - unsigned long val, void *data)
> -{
> - struct cpufreq_policy *policy = data;
> - int cpu;
> -
> - if (val != CPUFREQ_CREATE_POLICY)
> - return NOTIFY_DONE;
> -
> - /*
> - * Let each online CPU related to the policy update the period by their
> - * own. This will serialize with the framework on start/stop the lockup
> - * detector (softlockup_{start,stop}_all) and avoid potential race
> - * condition. Otherwise we may have below theoretical race condition:
> - * (core 0/1 share the same policy)
> - * [core 0] [core 1]
> - * hardlockup_detector_event_create()
> - * hw_nmi_get_sample_period()
> - * (cpufreq registered, notifier callback invoked)
> - * watchdog_freq_notifier_callback()
> - * watchdog_perf_update_period()
> - * (since core 1's event's not yet created,
> - * the period is not set)
> - * perf_event_create_kernel_counter()
> - * (event's period is SAFE_MAX_CPU_FREQ)
> - */
> - for_each_cpu(cpu, policy->cpus)
> - smp_call_on_cpu(cpu, watchdog_perf_update_period, NULL, false);
> -
> - return NOTIFY_DONE;
> -}
> -
> -static struct notifier_block watchdog_freq_notifier = {
> - .notifier_call = watchdog_freq_notifier_callback,
> -};
> -
> -static int __init init_watchdog_freq_notifier(void)
> -{
> - return cpufreq_register_notifier(&watchdog_freq_notifier,
> - CPUFREQ_POLICY_NOTIFIER);
> -}
> -core_initcall(init_watchdog_freq_notifier);
> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> index 973a027d90639..294a5c3438ad1 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -17,6 +17,7 @@
> #include <linux/cpu_pm.h>
> #include <linux/export.h>
> #include <linux/kernel.h>
> +#include <linux/nmi.h>
> #include <linux/perf/arm_pmu.h>
> #include <linux/slab.h>
> #include <linux/sched/clock.h>
> @@ -703,10 +704,17 @@ static int armpmu_get_cpu_irq(struct arm_pmu *pmu, int cpu)
> return per_cpu(hw_events->irq, cpu);
> }
>
> -bool arm_pmu_irq_is_nmi(void)
> +#ifdef CONFIG_HARDLOCKUP_DETECTOR_PERF
> +bool arch_perf_nmi_is_available(void)
> {
> + /*
> + * watchdog_hardlockup_probe() will success even if Pseudo-NMI turns off,
> + * however, the pmu interrupts will act like a normal interrupt instead of
> + * NMI and the hardlockup detector would be broken.
> + */
the comment makes me a bit confused. we'll only declare the NMI support if we successfully
registered the PMU interrupt as NMI interrupt. If pseudo-nmi is turned off, we'll
failed to register the NMI interrupt since neither the gicv3 irqchip will declare NMI
suppport [1] nor the irq_chip::irq_nmi_setup() will success [2], then the has_nmi will
be false. In this case the hardlockup detector is not probed at all [3].
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/irqchip/irq-gic-v3.c#n1956
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/irqchip/irq-gic-v3.c#n602
[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/watchdog_perf.c#n268
> return has_nmi;
> }
> +#endif
>
> /*
> * PMU hardware loses all context when a CPU goes offline.
> diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
> index 52b37f7bdbf9e..8f06751f1e176 100644
> --- a/include/linux/perf/arm_pmu.h
> +++ b/include/linux/perf/arm_pmu.h
> @@ -183,8 +183,6 @@ void kvm_host_pmu_init(struct arm_pmu *pmu);
> #define kvm_host_pmu_init(x) do { } while(0)
> #endif
>
> -bool arm_pmu_irq_is_nmi(void);
> -
> /* Internal functions only for core arm_pmu code */
> struct arm_pmu *armpmu_alloc(void);
> void armpmu_free(struct arm_pmu *pmu);
> diff --git a/kernel/watchdog_perf.c b/kernel/watchdog_perf.c
> index d3ca70e3c256a..8aa5e9a0ba20a 100644
> --- a/kernel/watchdog_perf.c
> +++ b/kernel/watchdog_perf.c
> @@ -15,6 +15,7 @@
> #include <linux/panic.h>
> #include <linux/nmi.h>
> #include <linux/atomic.h>
> +#include <linux/cpufreq.h>
> #include <linux/module.h>
> #include <linux/sched/debug.h>
>
> @@ -306,3 +307,85 @@ void __init hardlockup_config_perf_event(const char *str)
> wd_hw_attr.type = PERF_TYPE_RAW;
> wd_hw_attr.config = config;
> }
> +
> +#ifdef CONFIG_WATCHDOG_PERF_ADJUST_PERIOD
> +/*
> + * Safe maximum CPU frequency in case a particular platform doesn't implement
> + * cpufreq driver. Although, architecture doesn't put any restrictions on
> + * maximum frequency but 5 GHz seems to be safe maximum given the available
> + * CPUs in the market which are clocked much less than 5 GHz. On the other
> + * hand, we can't make it much higher as it would lead to a large hard-lockup
> + * detection timeout on parts which are running slower (eg. 1GHz on
> + * Developerbox) and doesn't possess a cpufreq driver.
> + */
> +#define SAFE_MAX_CPU_FREQ 5000000000UL // 5 GHz
> +u64 hw_nmi_get_sample_period(int watchdog_thresh)
> +{
> + unsigned int cpu = smp_processor_id();
> + unsigned long max_cpu_freq;
> +
> + max_cpu_freq = cpufreq_get_hw_max_freq(cpu) * 1000UL;
> + if (!max_cpu_freq)
> + max_cpu_freq = SAFE_MAX_CPU_FREQ;
> +
> + return (u64)max_cpu_freq * watchdog_thresh;
> +}
> +
> +static int watchdog_perf_update_period(void *data)
> +{
> + int cpu = smp_processor_id();
> + u64 max_cpu_freq, new_period;
> +
> + max_cpu_freq = cpufreq_get_hw_max_freq(cpu) * 1000UL;
> + if (!max_cpu_freq)
> + return 0;
> +
> + new_period = watchdog_thresh * max_cpu_freq;
> + hardlockup_detector_perf_adjust_period(new_period);
> +
> + return 0;
> +}
> +
> +static int watchdog_freq_notifier_callback(struct notifier_block *nb,
> + unsigned long val, void *data)
> +{
> + struct cpufreq_policy *policy = data;
> + int cpu;
> +
> + if (val != CPUFREQ_CREATE_POLICY)
> + return NOTIFY_DONE;
> +
> + /*
> + * Let each online CPU related to the policy update the period by their
> + * own. This will serialize with the framework on start/stop the lockup
> + * detector (softlockup_{start,stop}_all) and avoid potential race
> + * condition. Otherwise we may have below theoretical race condition:
> + * (core 0/1 share the same policy)
> + * [core 0] [core 1]
> + * hardlockup_detector_event_create()
> + * hw_nmi_get_sample_period()
> + * (cpufreq registered, notifier callback invoked)
> + * watchdog_freq_notifier_callback()
> + * watchdog_perf_update_period()
> + * (since core 1's event's not yet created,
> + * the period is not set)
> + * perf_event_create_kernel_counter()
> + * (event's period is SAFE_MAX_CPU_FREQ)
> + */
> + for_each_cpu(cpu, policy->cpus)
> + smp_call_on_cpu(cpu, watchdog_perf_update_period, NULL, false);
> +
> + return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block watchdog_freq_notifier = {
> + .notifier_call = watchdog_freq_notifier_callback,
> +};
> +
> +static int __init init_watchdog_freq_notifier(void)
> +{
> + return cpufreq_register_notifier(&watchdog_freq_notifier,
> + CPUFREQ_POLICY_NOTIFIER);
> +}
> +core_initcall(init_watchdog_freq_notifier);
> +#endif
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 2cbfa3dead0be..85fdfa9b52346 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1193,6 +1193,14 @@ config HARDLOCKUP_DETECTOR_PERF
> depends on !HAVE_HARDLOCKUP_DETECTOR_ARCH
> select HARDLOCKUP_DETECTOR_COUNTS_HRTIMER
>
> +config WATCHDOG_PERF_ADJUST_PERIOD
> + bool
it's reasonable to make it depends on HARDLOCKUP_DETECTOR_PERF.
otherwise looks good to me :)
Thanks.
> + help
> + Adjust the watchdog hardlockup detector's period based on CPU max
> + frequency. Uses cpufreq if available; falls back to a safe 5 GHz
> + default otherwise. Registers a cpufreq notifier to update the period
> + automatically.
> +
> config HARDLOCKUP_DETECTOR_BUDDY
> bool
> depends on HARDLOCKUP_DETECTOR
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