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Message-ID: <b5d88f82-6048-4ca9-becb-3e2c68acbaaf@linux.alibaba.com>
Date: Wed, 31 Jan 2024 19:08:36 +0800
From: Bitao Hu <yaoma@...ux.alibaba.com>
To: Liu Song <liusong@...ux.alibaba.com>, dianders@...omium.org,
akpm@...ux-foundation.org, pmladek@...e.com, lecopzer.chen@...iatek.com,
kernelfans@...il.com
Cc: linux-kernel@...r.kernel.org, yaoma@...ux.alibaba.com
Subject: Re: [PATCHv2 2/2] watchdog/softlockup: report the most frequent
interrupts
On 2024/1/31 09:50, Liu Song wrote:
>
> 在 2024/1/30 15:47, 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 | 150 ++++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 150 insertions(+)
>>
>> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
>> index 0efe9604c3c2..38fb18e17d71 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;
>> @@ -457,6 +464,8 @@ static enum cpu_usage_stat
>> idx_to_stat[NUM_STATS_PER_GROUP] = {
>> CPUTIME_SYSTEM, CPUTIME_SOFTIRQ, CPUTIME_IRQ, CPUTIME_IDLE
>> };
>> +static void print_hardirq_counts(void);
>> +
>> static void update_cpustat(void)
>> {
>> u8 i;
>> @@ -504,10 +513,150 @@ static void print_cpustat(void)
>> utilization[i][STATS_SYSTEM],
>> utilization[i][STATS_SOFTIRQ],
>> utilization[i][STATS_HARDIRQ], 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);
>> +
>> +static void find_counts_top(u32 *irq_counts, int *irq, u32
>> perirq_counts, int perirq_id, int range)
>> +{
>> + unsigned int i, j;
>> +
>> + for (i = 0; i < range; i++) {
>> + if (perirq_counts > irq_counts[i]) {
>> + for (j = range - 1; j > i; j--) {
>> + irq_counts[j] = irq_counts[j - 1];
>> + irq[j] = irq[j - 1];
>> + }
>> + irq_counts[j] = perirq_counts;
>> + irq[j] = perirq_id;
>> + break;
>> + }
>> + }
>> +}
>> +
>> +/*
>> + * 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();
>> +}
>> +
>> +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();
>> + u32 hardirq_counts_top[NUM_HARDIRQ_REPORT] = {0, 0, 0, 0, 0};
>> + int hardirq_top[NUM_HARDIRQ_REPORT] = {-1, -1, -1, -1, -1};
> "hardirq_counts_top" and "hardirq_top" seem like two members of a struct,
> working together to record the most suspicious irq, so wouldn't using a
> struct make it clearer?
OK, I will define a struct.
>> +
>> + 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, hardirq_top,
>> + counts_diff, i, 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_top[i] == -1)
>> + break;
>> + desc = irq_to_desc(hardirq_top[i]);
>> + if (desc && desc->action)
>> + printk(KERN_CRIT "\t#%u: %-10u\tirq#%d(%s)\n",
>> + i+1, hardirq_counts_top[i],
>> + hardirq_top[i], desc->action->name);
>> + else
>> + printk(KERN_CRIT "\t#%u: %-10u\tirq#%d\n",
>> + i+1, hardirq_counts_top[i],
>> + hardirq_top[i]);
>> + }
>> + 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 */
>> @@ -525,6 +674,7 @@ 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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