| Message ID | 20240306125208.71803-5-yaoma@linux.alibaba.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | *** Detect interrupt storm in softlockup *** | expand |
On Wed, Mar 06 2024 at 20:52, Bitao Hu wrote: > + if (__this_cpu_read(snapshot_taken)) { > + for_each_active_irq(i) { > + count = kstat_get_irq_since_snapshot(i); > + tabulate_irq_count(irq_counts_sorted, i, count, NUM_HARDIRQ_REPORT); > + } > + > + /* > + * We do not want the "watchdog: " prefix on every line, > + * hence we use "printk" instead of "pr_crit". > + */ You are not providing any justification why the prefix is not wanted. Just saying 'We do not want' does not cut it and who is 'We'. I certainly not. I really disagree because the prefixes are very useful for searching log files. So not having it makes it harder to filter out for no reason. Thanks, tglx
Hi, Thomas On 2024/3/24 04:43, Thomas Gleixner wrote: > On Wed, Mar 06 2024 at 20:52, Bitao Hu wrote: >> + if (__this_cpu_read(snapshot_taken)) { >> + for_each_active_irq(i) { >> + count = kstat_get_irq_since_snapshot(i); >> + tabulate_irq_count(irq_counts_sorted, i, count, NUM_HARDIRQ_REPORT); >> + } >> + >> + /* >> + * We do not want the "watchdog: " prefix on every line, >> + * hence we use "printk" instead of "pr_crit". >> + */ > > You are not providing any justification why the prefix is not > wanted. Just saying 'We do not want' does not cut it and who is 'We'. I > certainly not. > > I really disagree because the prefixes are very useful for searching log > files. So not having it makes it harder to filter out for no reason. > Regarding the use of printk() instead of pr_crit(), I have had a discussion with Liu Song and Douglas in PATCHv1: https://lore.kernel.org/all/CAD=FV=WEEQeKX=ec3Gr-8CKs2K0MaWN3V0-0yOsuret0qcB_AA@mail.gmail.com/ Please allow me to elaborate on my reasoning. The purpose of the report_cpu_status() function I implemented is similar to that of print_modules(), show_regs(), and dump_stack(). These functions are designed to assist in analyzing the causes of a soft lockup, rather than to report that a soft lockup has occurred. Therefore, I think that adding the "watchdog: " prefix to every line is redundant and not concise. Besides, the existing pr_emerg() in the watchdog.c file is already sufficient for searching useful information in the logs. The information I added, along with the call tree and other data, is located near the line with the "watchdog: " prefix. Are the two reasons I've provided reasonable? Best Regards, Bitao Hu
Hi, On Mon, Mar 25, 2024 at 2:48 AM Bitao Hu <yaoma@linux.alibaba.com> wrote: > > Hi, Thomas > > On 2024/3/24 04:43, Thomas Gleixner wrote: > > On Wed, Mar 06 2024 at 20:52, Bitao Hu wrote: > >> + if (__this_cpu_read(snapshot_taken)) { > >> + for_each_active_irq(i) { > >> + count = kstat_get_irq_since_snapshot(i); > >> + tabulate_irq_count(irq_counts_sorted, i, count, NUM_HARDIRQ_REPORT); > >> + } > >> + > >> + /* > >> + * We do not want the "watchdog: " prefix on every line, > >> + * hence we use "printk" instead of "pr_crit". > >> + */ > > > > You are not providing any justification why the prefix is not > > wanted. Just saying 'We do not want' does not cut it and who is 'We'. I > > certainly not. > > > > I really disagree because the prefixes are very useful for searching log > > files. So not having it makes it harder to filter out for no reason. > > > > > Regarding the use of printk() instead of pr_crit(), I have had a > discussion with Liu Song and Douglas in PATCHv1: > https://lore.kernel.org/all/CAD=FV=WEEQeKX=ec3Gr-8CKs2K0MaWN3V0-0yOsuret0qcB_AA@mail.gmail.com/ > > Please allow me to elaborate on my reasoning. The purpose of the > report_cpu_status() function I implemented is similar to that of > print_modules(), show_regs(), and dump_stack(). These functions are > designed to assist in analyzing the causes of a soft lockup, rather > than to report that a soft lockup has occurred. Therefore, I think > that adding the "watchdog: " prefix to every line is redundant and > not concise. Besides, the existing pr_emerg() in the watchdog.c file > is already sufficient for searching useful information in the logs. > The information I added, along with the call tree and other data, is > located near the line with the "watchdog: " prefix. > > Are the two reasons I've provided reasonable? FWIW I don't feel super strongly about this, but I'm leaning towards agreeing with Bitao. The sample output from the commit message looks like this: [ 638.870231] watchdog: BUG: soft lockup - CPU#9 stuck for 26s! [swapper/9:0] [ 638.870825] CPU#9 Utilization every 4s during lockup: [ 638.871194] #1: 0% system, 0% softirq, 100% hardirq, 0% idle [ 638.871652] #2: 0% system, 0% softirq, 100% hardirq, 0% idle [ 638.872107] #3: 0% system, 0% softirq, 100% hardirq, 0% idle [ 638.872563] #4: 0% system, 0% softirq, 100% hardirq, 0% idle [ 638.873018] #5: 0% system, 0% softirq, 100% hardirq, 0% idle [ 638.873494] CPU#9 Detect HardIRQ Time exceeds 50%. Most frequent HardIRQs: [ 638.873994] #1: 330945 irq#7 [ 638.874236] #2: 31 irq#82 [ 638.874493] #3: 10 irq#10 [ 638.874744] #4: 2 irq#89 [ 638.874992] #5: 1 irq#102 ...and in my mind the "watchdog: BUG: soft lockup - CPU#9 stuck for 26s! [swapper/9:0]" line is enough to grep through the dmesg. Having all the following lines start with "watchdog:" feels like overkill to me, but if you feel strongly that they should then it wouldn't bother me too much for them all to have the "watchdog:" prefix. Could you clarify how strongly you feel about this and whether Bitao should spin a v13? I believe that this is the only point of contention on the patch series right now and otherwise it could be ready to land. I know in the past Petr has wanted ample time to comment though perhaps the fact that it's been ~1 month is enough. Petr: do you have anything that needs saying before this patch series lands? Thanks! -Doug
diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 69e72d7e461d..c9d49ae8d045 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -12,22 +12,25 @@ #define pr_fmt(fmt) "watchdog: " fmt -#include <linux/mm.h> #include <linux/cpu.h> -#include <linux/nmi.h> #include <linux/init.h> +#include <linux/irq.h> +#include <linux/irqdesc.h> #include <linux/kernel_stat.h> +#include <linux/kvm_para.h> #include <linux/math64.h> +#include <linux/mm.h> #include <linux/module.h> +#include <linux/nmi.h> +#include <linux/stop_machine.h> #include <linux/sysctl.h> #include <linux/tick.h> + #include <linux/sched/clock.h> #include <linux/sched/debug.h> #include <linux/sched/isolation.h> -#include <linux/stop_machine.h> #include <asm/irq_regs.h> -#include <linux/kvm_para.h> static DEFINE_MUTEX(watchdog_mutex); @@ -417,13 +420,104 @@ static void print_cpustat(void) } } +#define HARDIRQ_PERCENT_THRESH 50 +#define NUM_HARDIRQ_REPORT 5 +struct irq_counts { + int irq; + u32 counts; +}; + +static DEFINE_PER_CPU(bool, snapshot_taken); + +/* Tabulate the most frequent interrupts. */ +static void tabulate_irq_count(struct irq_counts *irq_counts, int irq, u32 counts, int rank) +{ + int i; + struct irq_counts new_count = {irq, counts}; + + for (i = 0; i < rank; i++) { + if (counts > irq_counts[i].counts) + swap(new_count, irq_counts[i]); + } +} + +/* + * If the hardirq time exceeds HARDIRQ_PERCENT_THRESH% of the sample_period, + * then the cause of softlockup might be interrupt storm. In this case, it + * would be useful to start interrupt counting. + */ +static bool need_counting_irqs(void) +{ + u8 util; + int tail = __this_cpu_read(cpustat_tail); + + tail = (tail + NUM_HARDIRQ_REPORT - 1) % NUM_HARDIRQ_REPORT; + util = __this_cpu_read(cpustat_util[tail][STATS_HARDIRQ]); + return util > HARDIRQ_PERCENT_THRESH; +} + +static void start_counting_irqs(void) +{ + if (!__this_cpu_read(snapshot_taken)) { + kstat_snapshot_irqs(); + __this_cpu_write(snapshot_taken, true); + } +} + +static void stop_counting_irqs(void) +{ + __this_cpu_write(snapshot_taken, false); +} + +static void print_irq_counts(void) +{ + unsigned int i, count; + struct irq_counts irq_counts_sorted[NUM_HARDIRQ_REPORT] = { + {-1, 0}, {-1, 0}, {-1, 0}, {-1, 0}, {-1, 0} + }; + + if (__this_cpu_read(snapshot_taken)) { + for_each_active_irq(i) { + count = kstat_get_irq_since_snapshot(i); + tabulate_irq_count(irq_counts_sorted, i, count, 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 (irq_counts_sorted[i].irq == -1) + break; + + printk(KERN_CRIT "\t#%u: %-10u\tirq#%d\n", + i + 1, irq_counts_sorted[i].counts, + irq_counts_sorted[i].irq); + } + + /* + * If the hardirq time is less than HARDIRQ_PERCENT_THRESH% in the last + * sample_period, then we suspect the interrupt storm might be subsiding. + */ + if (!need_counting_irqs()) + stop_counting_irqs(); + } +} + static void report_cpu_status(void) { print_cpustat(); + print_irq_counts(); } #else static inline void update_cpustat(void) { } static inline void report_cpu_status(void) { } +static inline bool need_counting_irqs(void) { return false; } +static inline void start_counting_irqs(void) { } +static inline void stop_counting_irqs(void) { } #endif /* @@ -527,6 +621,18 @@ static int is_softlockup(unsigned long touch_ts, unsigned long now) { if ((watchdog_enabled & WATCHDOG_SOFTOCKUP_ENABLED) && watchdog_thresh) { + /* + * If period_ts has not been updated during a sample_period, then + * in the subsequent few sample_periods, period_ts might also not + * be updated, which could indicate a potential softlockup. In + * this case, if we suspect the cause of the potential softlockup + * might be interrupt storm, then we need to count the interrupts + * to find which interrupt is storming. + */ + if (time_after_eq(now, period_ts + get_softlockup_thresh() / NUM_SAMPLE_PERIODS) && + need_counting_irqs()) + start_counting_irqs(); + /* Warn about unreasonable delays. */ if (time_after(now, period_ts + get_softlockup_thresh())) return now - touch_ts; @@ -549,6 +655,7 @@ static DEFINE_PER_CPU(struct cpu_stop_work, softlockup_stop_work); static int softlockup_fn(void *data) { update_touch_ts(); + stop_counting_irqs(); complete(this_cpu_ptr(&softlockup_completion)); return 0;