linux-kernel - [PATCH v7 5/6] arm64: add hw_nmi_get_sample_period for preparation of lockup detector

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Date:   Sat, 3 Sep 2022 17:34:14 +0800
From:   Lecopzer Chen <lecopzer.chen@...iatek.com>
To:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-perf-users@...r.kernel.org>,
        <mark.rutland@....com>, <will@...nel.org>
CC:     <lecopzer.chen@...iatek.com>, <acme@...nel.org>,
        <akpm@...ux-foundation.org>, <alexander.shishkin@...ux.intel.com>,
        <catalin.marinas@....com>, <davem@...emloft.net>,
        <jolsa@...hat.com>, <jthierry@...hat.com>, <keescook@...omium.org>,
        <kernelfans@...il.com>, <masahiroy@...nel.org>,
        <matthias.bgg@...il.com>, <maz@...nel.org>, <mcgrof@...nel.org>,
        <mingo@...hat.com>, <namhyung@...nel.org>, <nixiaoming@...wei.com>,
        <peterz@...radead.org>, <pmladek@...e.com>,
        <sparclinux@...r.kernel.org>, <sumit.garg@...aro.org>,
        <wangqing@...o.com>, <yj.chiang@...iatek.com>
Subject: [PATCH v7 5/6] arm64: add hw_nmi_get_sample_period for preparation of lockup detector

Set safe maximum CPU frequency to 5 GHz 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.

[1]:http://lore.kernel.org/linux-arm-kernel/1610712101-14929-1-git-send-email-sumit.garg@linaro.org

Co-developed-by: Sumit Garg <sumit.garg@...aro.org>
Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
Co-developed-by: Pingfan Liu <kernelfans@...il.com>
Signed-off-by: Pingfan Liu <kernelfans@...il.com>
Signed-off-by: Lecopzer Chen <lecopzer.chen@...iatek.com>
---
 arch/arm64/kernel/Makefile       |  1 +
 arch/arm64/kernel/watchdog_hld.c | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+)
 create mode 100644 arch/arm64/kernel/watchdog_hld.c

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 1add7b01efa7..122b50bfcc0e 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -51,6 +51,7 @@ obj-$(CONFIG_MODULES)			+= module.o
 obj-$(CONFIG_ARM64_MODULE_PLTS)		+= module-plts.o
 obj-$(CONFIG_PERF_EVENTS)		+= perf_regs.o perf_callchain.o
 obj-$(CONFIG_HW_PERF_EVENTS)		+= perf_event.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_CPU_IDLE)			+= cpuidle.o
diff --git a/arch/arm64/kernel/watchdog_hld.c b/arch/arm64/kernel/watchdog_hld.c
new file mode 100644
index 000000000000..de43318e4dd6
--- /dev/null
+++ b/arch/arm64/kernel/watchdog_hld.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/cpufreq.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;
+}
+
-- 
2.34.1