Messages in this thread | | | Date | Wed, 31 Jan 2024 09:19:35 +0800 | Subject | Re: [PATCHv2 1/2] watchdog/softlockup: low-overhead detection of interrupt storm | From | Liu Song <> |
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在 2024/1/30 15:47, Bitao Hu 写道: > The following softlockup is caused by interrupt storm, but it cannot be > identified from the call tree. Because the call tree is just a snapshot > and doesn't fully capture the behavior of the CPU during the soft lockup. > watchdog: BUG: soft lockup - CPU#28 stuck for 23s! [fio:83921] > ... > Call trace: > __do_softirq+0xa0/0x37c > __irq_exit_rcu+0x108/0x140 > irq_exit+0x14/0x20 > __handle_domain_irq+0x84/0xe0 > gic_handle_irq+0x80/0x108 > el0_irq_naked+0x50/0x58 > > Therefore,I think it is necessary to report CPU utilization during the > softlockup_thresh period (report once every sample_period, for a total > of 5 reportings), like this: > watchdog: BUG: soft lockup - CPU#28 stuck for 23s! [fio:83921] > CPU#28 Utilization every 4s during lockup: > #1: 0% system, 0% softirq, 100% hardirq, 0% idle > #2: 0% system, 0% softirq, 100% hardirq, 0% idle > #3: 0% system, 0% softirq, 100% hardirq, 0% idle > #4: 0% system, 0% softirq, 100% hardirq, 0% idle > #5: 0% system, 0% softirq, 100% hardirq, 0% idle > ... > > This would be helpful in determining whether an interrupt storm has > occurred or in identifying the cause of the softlockup. The criteria for > determination are as follows: > a. If the hardirq utilization is high, then interrupt storm should be > considered and the root cause cannot be determined from the call tree. > b. If the softirq utilization is high, then we could analyze the call > tree but it may cannot reflect the root cause. > c. If the system utilization is high, then we could analyze the root > cause from the call tree. > > Signed-off-by: Bitao Hu <yaoma@linux.alibaba.com> > --- > kernel/watchdog.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 72 insertions(+) > > diff --git a/kernel/watchdog.c b/kernel/watchdog.c > index 81a8862295d6..0efe9604c3c2 100644 > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -23,6 +23,8 @@ > #include <linux/sched/debug.h> > #include <linux/sched/isolation.h> > #include <linux/stop_machine.h> > +#include <linux/kernel_stat.h> > +#include <linux/math64.h> > > #include <asm/irq_regs.h> > #include <linux/kvm_para.h> > @@ -441,6 +443,73 @@ static int is_softlockup(unsigned long touch_ts, > return 0; > } > > +#ifdef CONFIG_IRQ_TIME_ACCOUNTING > +#define NUM_STATS_GROUPS 5 > +#define STATS_SYSTEM 0 > +#define STATS_SOFTIRQ 1 > +#define STATS_HARDIRQ 2 > +#define STATS_IDLE 3 > +#define NUM_STATS_PER_GROUP 4 This is a set of related numbers; wouldn't it be better to use an enum? > +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 enum cpu_usage_stat idx_to_stat[NUM_STATS_PER_GROUP] = { > + CPUTIME_SYSTEM, CPUTIME_SOFTIRQ, CPUTIME_IRQ, CPUTIME_IDLE > +}; To be honest, I'm not particularly fond of the name 'idx_to_stat' as the concept of an index is already implied by the nature of an array, so adding 'idx' is redundant. I suggest shortening the name.
> + > +static void update_cpustat(void) > +{ > + u8 i; > + u16 *old = this_cpu_ptr(cpustat_old); > + u8 (*utilization)[NUM_STATS_PER_GROUP] = this_cpu_ptr(cpustat_utilization); > + u8 tail = this_cpu_read(cpustat_tail); > + struct kernel_cpustat kcpustat; > + u64 *cpustat = kcpustat.cpustat; > + u16 sample_period_ms = sample_period >> 24LL; /* 2^24ns ~= 16.8ms */
There are two instances where right shift operations are used; it is suggested to employ a helper macro for a more comfortable look.
> + > + kcpustat_cpu_fetch(&kcpustat, smp_processor_id()); > + for (i = STATS_SYSTEM; i < NUM_STATS_PER_GROUP; i++) { > + /* > + * We don't need nanosecond resolution. A granularity of 16ms is > + * sufficient for our precision, allowing us to use u16 to store > + * cpustats, which will roll over roughly every ~1000 seconds. > + * 2^24 ~= 16 * 10^6 > + */ > + cpustat[idx_to_stat[i]] = lower_16_bits(cpustat[idx_to_stat[i]] >> 24LL); > + utilization[tail][i] = 100 * (u16)(cpustat[idx_to_stat[i]] - old[i]) > + / sample_period_ms; > + old[i] = cpustat[idx_to_stat[i]]; > + } > + this_cpu_write(cpustat_tail, (tail + 1) % NUM_STATS_GROUPS); > +} > + > +static void print_cpustat(void) > +{ > + u8 i, j; > + u8 (*utilization)[NUM_STATS_PER_GROUP] = this_cpu_ptr(cpustat_utilization); > + u8 tail = this_cpu_read(cpustat_tail); > + u64 sample_period_second = sample_period; > + > + do_div(sample_period_second, NSEC_PER_SEC); > + /* > + * We do not want the "watchdog: " prefix on every line, > + * hence we use "printk" instead of "pr_crit". > + */ > + printk(KERN_CRIT "CPU#%d Utilization every %llus during lockup:\n", > + smp_processor_id(), sample_period_second); > + for (j = STATS_SYSTEM, i = tail; j < NUM_STATS_GROUPS; > + j++, i = (i + 1) % NUM_STATS_GROUPS) { > + printk(KERN_CRIT "\t#%d: %3u%% system,\t%3u%% softirq,\t" > + "%3u%% hardirq,\t%3u%% idle\n", j+1, > + utilization[i][STATS_SYSTEM], utilization[i][STATS_SOFTIRQ], > + utilization[i][STATS_HARDIRQ], utilization[i][STATS_IDLE]); > + } > +} > +#else > +static inline void update_cpustat(void) { } > +static inline void print_cpustat(void) { } > +#endif > + > /* watchdog detector functions */ > static DEFINE_PER_CPU(struct completion, softlockup_completion); > static DEFINE_PER_CPU(struct cpu_stop_work, softlockup_stop_work); > @@ -504,6 +573,8 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) > */ > period_ts = READ_ONCE(*this_cpu_ptr(&watchdog_report_ts)); > > + update_cpustat(); > + > /* Reset the interval when touched by known problematic code. */ > if (period_ts == SOFTLOCKUP_DELAY_REPORT) { > if (unlikely(__this_cpu_read(softlockup_touch_sync))) { > @@ -539,6 +610,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) > pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n", > smp_processor_id(), duration, > current->comm, task_pid_nr(current)); > + print_cpustat(); > print_modules(); > print_irqtrace_events(current); > if (regs)
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