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Date: Thu, 1 Feb 2024 09:46:48 +0800
From: Liu Song <liusong@...ux.alibaba.com>
To: Bitao Hu <yaoma@...ux.alibaba.com>, dianders@...omium.org,
akpm@...ux-foundation.org, pmladek@...e.com, kernelfans@...il.com
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 2/2] watchdog/softlockup: report the most frequent
interrupts
在 2024/2/1 01:17, Bitao Hu 写道:
> When the watchdog determines that the current soft lockup is due
> to an interrupt storm based on CPU utilization, reporting the
> most frequent interrupts could be good enough for further
> troubleshooting.
>
> Below is an example of interrupt storm. The call tree does not
> provide useful information, but we can analyze which interrupt
> caused the soft lockup by comparing the counts of interrupts.
>
> [ 2987.488075] watchdog: BUG: soft lockup - CPU#9 stuck for 23s! [kworker/9:1:214]
> [ 2987.488607] CPU#9 Utilization every 4s during lockup:
> [ 2987.488941] #1: 0% system, 0% softirq, 100% hardirq, 0% idle
> [ 2987.489357] #2: 0% system, 0% softirq, 100% hardirq, 0% idle
> [ 2987.489771] #3: 0% system, 0% softirq, 100% hardirq, 0% idle
> [ 2987.490186] #4: 0% system, 0% softirq, 100% hardirq, 0% idle
> [ 2987.490601] #5: 0% system, 0% softirq, 100% hardirq, 0% idle
> [ 2987.491034] CPU#9 Detect HardIRQ Time exceeds 50%. Most frequent HardIRQs:
> [ 2987.491493] #1: 330985 irq#7(IPI)
> [ 2987.491743] #2: 5000 irq#10(arch_timer)
> [ 2987.492039] #3: 9 irq#91(nvme0q2)
> [ 2987.492318] #4: 3 irq#118(virtio1-output.12)
> ...
> [ 2987.492728] Call trace:
> [ 2987.492729] __do_softirq+0xa8/0x364
>
> Signed-off-by: Bitao Hu <yaoma@...ux.alibaba.com>
> ---
> kernel/watchdog.c | 156 ++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 156 insertions(+)
>
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 046507be4eb5..c4c25f25eae7 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -25,6 +25,9 @@
> #include <linux/stop_machine.h>
> #include <linux/kernel_stat.h>
> #include <linux/math64.h>
> +#include <linux/irq.h>
> +#include <linux/bitops.h>
> +#include <linux/irqdesc.h>
>
> #include <asm/irq_regs.h>
> #include <linux/kvm_para.h>
> @@ -431,11 +434,15 @@ void touch_softlockup_watchdog_sync(void)
> __this_cpu_write(watchdog_report_ts, SOFTLOCKUP_DELAY_REPORT);
> }
>
> +static void set_potential_softlockup(unsigned long now, unsigned long touch_ts);
> +
> static int is_softlockup(unsigned long touch_ts,
> unsigned long period_ts,
> unsigned long now)
> {
> if ((watchdog_enabled & WATCHDOG_SOFTOCKUP_ENABLED) && watchdog_thresh) {
> + /* Softlockup may occur in the current period */
> + set_potential_softlockup(now, period_ts);
> /* Warn about unreasonable delays. */
> if (time_after(now, period_ts + get_softlockup_thresh()))
> return now - touch_ts;
> @@ -462,6 +469,8 @@ static DEFINE_PER_CPU(u16, cpustat_old[NUM_STATS_PER_GROUP]);
> static DEFINE_PER_CPU(u8, cpustat_utilization[NUM_STATS_GROUPS][NUM_STATS_PER_GROUP]);
> static DEFINE_PER_CPU(u8, cpustat_tail);
>
> +static void print_hardirq_counts(void);
> +
> /*
> * We don't need nanosecond resolution. A granularity of 16ms is
> * sufficient for our precision, allowing us to use u16 to store
> @@ -516,10 +525,156 @@ static void print_cpustat(void)
> __this_cpu_read(cpustat_utilization[i][STATS_HARDIRQ]),
> __this_cpu_read(cpustat_utilization[i][STATS_IDLE]));
> }
> + print_hardirq_counts();
> +}
> +
> +#define HARDIRQ_PERCENT_THRESH 50
> +#define NUM_HARDIRQ_REPORT 5
> +static DECLARE_BITMAP(softlockup_hardirq_cpus, CONFIG_NR_CPUS);
> +static DEFINE_PER_CPU(u32 *, hardirq_counts);
> +
> +struct irq_counts {
> + int irq;
> + u32 counts;
> +};
> +
> +static void find_counts_top(struct irq_counts *irq_counts, int irq, u32 counts, int range)
> +{
> + unsigned int i, j;
> +
> + for (i = 0; i < range; i++) {
> + if (counts > irq_counts[i].counts) {
> + for (j = range - 1; j > i; j--) {
> + irq_counts[j].counts = irq_counts[j - 1].counts;
> + irq_counts[j].irq = irq_counts[j - 1].irq;
> + }
> + irq_counts[j].counts = counts;
> + irq_counts[j].irq = irq;
> + break;
> + }
The current implementation can lead to a reordering with each iteration.
It is recommended to update in place if the value is larger and perform
the reordering just before printing at the end.
> + }
> +}
> +
> +/*
> + * If the proportion of time spent handling irq exceeds HARDIRQ_PERCENT_THRESH%
> + * during sample_period, then it is necessary to record the counts of each irq.
> + */
> +static inline bool need_record_irq_counts(int type)
> +{
> + int tail = __this_cpu_read(cpustat_tail);
> + u8 utilization;
> +
> + if (--tail == -1)
> + tail = 4;
> + utilization = __this_cpu_read(cpustat_utilization[tail][type]);
> + return utilization > HARDIRQ_PERCENT_THRESH;
> +}
> +
> +/*
> + * Mark softlockup as potentially caused by hardirq
> + */
> +static void set_potential_softlockup_hardirq(void)
> +{
> + u32 i;
> + u32 *counts = __this_cpu_read(hardirq_counts);
> + int cpu = smp_processor_id();
> + struct irq_desc *desc;
> +
> + if (!need_record_irq_counts(STATS_HARDIRQ))
> + return;
> +
> + if (!test_bit(cpu, softlockup_hardirq_cpus)) {
> + counts = kmalloc_array(nr_irqs, sizeof(u32), GFP_ATOMIC);
> + if (!counts)
> + return;
> + for_each_irq_desc(i, desc) {
> + if (!desc)
> + continue;
> + counts[i] = desc->kstat_irqs ?
> + *this_cpu_ptr(desc->kstat_irqs) : 0;
> + }
> + __this_cpu_write(hardirq_counts, counts);
> + set_bit(cpu, softlockup_hardirq_cpus);
> + }
> +}
> +
> +static void clear_potential_softlockup_hardirq(void)
> +{
> + u32 *counts = __this_cpu_read(hardirq_counts);
> + int cpu = smp_processor_id();
> +
> + if (test_bit(cpu, softlockup_hardirq_cpus)) {
> + kfree(counts);
> + counts = NULL;
> + __this_cpu_write(hardirq_counts, counts);
> + clear_bit(cpu, softlockup_hardirq_cpus);
> + }
> }
> +
> +/*
> + * Mark that softlockup may occur
> + */
> +static void set_potential_softlockup(unsigned long now, unsigned long period_ts)
> +{
> + if (time_after_eq(now, period_ts + get_softlockup_thresh() / 5))
> + set_potential_softlockup_hardirq();
> +}
> +
> +static void clear_potential_softlockup(void)
> +{
> + clear_potential_softlockup_hardirq();
> +}
Given that clear_potential_softlockup will only call
clear_potential_softlockup_hardirq, then why is there a need to declare
clear_potential_softlockup separately?
> +
> +static void print_hardirq_counts(void)
> +{
> + u32 i;
> + struct irq_desc *desc;
> + u32 counts_diff;
> + u32 *counts = __this_cpu_read(hardirq_counts);
> + int cpu = smp_processor_id();
> + struct irq_counts hardirq_counts_top[NUM_HARDIRQ_REPORT] = {
> + {-1, 0}, {-1, 0}, {-1, 0}, {-1, 0},
> + };
> +
> + if (test_bit(cpu, softlockup_hardirq_cpus)) {
> + /* Find the top NUM_HARDIRQ_REPORT most frequent interrupts */
> + for_each_irq_desc(i, desc) {
> + if (!desc)
> + continue;
> + counts_diff = desc->kstat_irqs ?
> + *this_cpu_ptr(desc->kstat_irqs) - counts[i] : 0;
> + find_counts_top(hardirq_counts_top, i, counts_diff,
> + NUM_HARDIRQ_REPORT);
> + }
> + /*
> + * We do not want the "watchdog: " prefix on every line,
> + * hence we use "printk" instead of "pr_crit".
> + */
> + printk(KERN_CRIT "CPU#%d Detect HardIRQ Time exceeds %d%%. Most frequent HardIRQs:\n",
> + smp_processor_id(), HARDIRQ_PERCENT_THRESH);
> + for (i = 0; i < NUM_HARDIRQ_REPORT; i++) {
> + if (hardirq_counts_top[i].irq == -1)
> + break;
> + desc = irq_to_desc(hardirq_counts_top[i].irq);
> + if (desc && desc->action)
> + printk(KERN_CRIT "\t#%u: %-10u\tirq#%d(%s)\n",
> + i+1, hardirq_counts_top[i].counts,
> + hardirq_counts_top[i].irq, desc->action->name);
> + else
> + printk(KERN_CRIT "\t#%u: %-10u\tirq#%d\n",
> + i+1, hardirq_counts_top[i].counts,
> + hardirq_counts_top[i].irq);
> + }
> + if (!need_record_irq_counts(STATS_HARDIRQ))
> + clear_potential_softlockup_hardirq();
> + }
> +}
> +
> #else
> static inline void update_cpustat(void) { }
> static inline void print_cpustat(void) { }
> +static inline void set_potential_softlockup(unsigned long now, unsigned long period_ts) { }
> +static inline void clear_potential_softlockup(void) { }
> #endif
>
> /* watchdog detector functions */
> @@ -537,6 +692,7 @@ static DEFINE_PER_CPU(struct cpu_stop_work, softlockup_stop_work);
> static int softlockup_fn(void *data)
> {
> update_touch_ts();
> + clear_potential_softlockup();
> complete(this_cpu_ptr(&softlockup_completion));
>
> return 0;
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