mainline inclusion from mainline-v6.3-rc1 commit be42f00b73a0f50710d16eb7cb4efda0cce062dd category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I7OIXK
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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Because RCU CPU stall warnings are driven from the scheduling-clock interrupt handler, a workload consisting of a very large number of short-duration hardware interrupts can result in misleading stall-warning messages. On systems supporting only a single level of interrupts, that is, where interrupts handlers cannot be interrupted, this can produce misleading diagnostics. The stack traces will show the innocent-bystander interrupted task, not the interrupts that are at the very least exacerbating the stall.
This situation can be improved by displaying the number of interrupts and the CPU time that they have consumed. Diagnosing other types of stalls can be eased by also providing the count of softirqs and the CPU time that they consumed as well as the number of context switches and the task-level CPU time consumed.
Consider the following output given this change:
rcu: INFO: rcu_preempt self-detected stall on CPU rcu: 0-....: (1250 ticks this GP) <omitted> rcu: hardirqs softirqs csw/system rcu: number: 624 45 0 rcu: cputime: 69 1 2425 ==> 2500(ms)
This output shows that the number of hard and soft interrupts is small, there are no context switches, and the system takes up a lot of time. This indicates that the current task is looping with preemption disabled.
The impact on system performance is negligible because snapshot is recorded only once for all continuous RCU stalls.
This added debugging information is suppressed by default and can be enabled by building the kernel with CONFIG_RCU_CPU_STALL_CPUTIME=y or by booting with rcupdate.rcu_cpu_stall_cputime=1.
Signed-off-by: Zhen Lei thunder.leizhen@huawei.com Reviewed-by: Mukesh Ojha quic_mojha@quicinc.com Reviewed-by: Frederic Weisbecker frederic@kernel.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Conflicts: Documentation/admin-guide/kernel-parameters.txt kernel/rcu/Kconfig.debug [Change RCU_CPU_STALL_CPUTIME to be enabled by default] kernel/rcu/rcu.h kernel/rcu/tree.h kernel/rcu/tree_stall.h kernel/rcu/update.c
Signed-off-by: Zhen Lei thunder.leizhen@huawei.com --- .../admin-guide/kernel-parameters.txt | 6 ++++ kernel/rcu/Kconfig.debug | 13 ++++++++ kernel/rcu/rcu.h | 1 + kernel/rcu/tree.c | 18 +++++++++++ kernel/rcu/tree.h | 19 ++++++++++++ kernel/rcu/tree_stall.h | 31 +++++++++++++++++++ kernel/rcu/update.c | 2 ++ 7 files changed, 90 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 2addbf715cc08f8..a47daa3af42cd95 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4695,6 +4695,12 @@ rcupdate.rcu_cpu_stall_timeout= [KNL] Set timeout for RCU CPU stall warning messages.
+ rcupdate.rcu_cpu_stall_cputime= [KNL] + Provide statistics on the cputime and count of + interrupts and tasks during the sampling period. For + multiple continuous RCU stalls, all sampling periods + begin at half of the first RCU stall timeout. + rcupdate.rcu_expedited= [KNL] Use expedited grace-period primitives, for example, synchronize_rcu_expedited() instead diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug index 1942c1f1bb65d32..65103e9fa6f84d7 100644 --- a/kernel/rcu/Kconfig.debug +++ b/kernel/rcu/Kconfig.debug @@ -91,6 +91,19 @@ config RCU_CPU_STALL_TIMEOUT RCU grace period persists, additional CPU stall warnings are printed at more widely spaced intervals.
+config RCU_CPU_STALL_CPUTIME + bool "Provide additional RCU stall debug information" + depends on RCU_STALL_COMMON + default n + help + Collect statistics during the sampling period, such as the number of + (hard interrupts, soft interrupts, task switches) and the cputime of + (hard interrupts, soft interrupts, kernel tasks) are added to the + RCU stall report. For multiple continuous RCU stalls, all sampling + periods begin at half of the first RCU stall timeout. + The boot option rcupdate.rcu_cpu_stall_cputime has the same function + as this one, but will override this if it exists. + config RCU_TRACE bool "Enable tracing for RCU" depends on DEBUG_KERNEL diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index fcf95d1eec69ab1..387c973e5c8134e 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -210,6 +210,7 @@ static inline bool rcu_stall_is_suppressed_at_boot(void) extern int rcu_cpu_stall_ftrace_dump; extern int rcu_cpu_stall_suppress; extern int rcu_cpu_stall_timeout; +extern int rcu_cpu_stall_cputime; int rcu_jiffies_till_stall_check(void);
static inline bool rcu_stall_is_suppressed(void) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 6a2669d1b6a2638..05a6a7bca03e10b 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1346,6 +1346,24 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) rdp->rcu_iw_gp_seq = rnp->gp_seq; irq_work_queue_on(&rdp->rcu_iw, rdp->cpu); } + + if (rcu_cpu_stall_cputime && rdp->snap_record.gp_seq != rdp->gp_seq) { + int cpu = rdp->cpu; + struct rcu_snap_record *rsrp; + struct kernel_cpustat *kcsp; + + kcsp = &kcpustat_cpu(cpu); + + rsrp = &rdp->snap_record; + rsrp->cputime_irq = kcpustat_field(kcsp, CPUTIME_IRQ, cpu); + rsrp->cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu); + rsrp->cputime_system = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu); + rsrp->nr_hardirqs = kstat_cpu_irqs_sum(rdp->cpu); + rsrp->nr_softirqs = kstat_cpu_softirqs_sum(rdp->cpu); + rsrp->nr_csw = nr_context_switches_cpu(rdp->cpu); + rsrp->jiffies = jiffies; + rsrp->gp_seq = rdp->gp_seq; + } }
return 0; diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index b64696ca9109845..2a68a9e0aea4709 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -147,6 +147,23 @@ union rcu_noqs { u16 s; /* Set of bits, aggregate OR here. */ };
+/* + * Record the snapshot of the core stats at half of the first RCU stall timeout. + * The member gp_seq is used to ensure that all members are updated only once + * during the sampling period. The snapshot is taken only if this gp_seq is not + * equal to rdp->gp_seq. + */ +struct rcu_snap_record { + unsigned long gp_seq; /* Track rdp->gp_seq counter */ + u64 cputime_irq; /* Accumulated cputime of hard irqs */ + u64 cputime_softirq;/* Accumulated cputime of soft irqs */ + u64 cputime_system; /* Accumulated cputime of kernel tasks */ + unsigned long nr_hardirqs; /* Accumulated number of hard irqs */ + unsigned int nr_softirqs; /* Accumulated number of soft irqs */ + unsigned long long nr_csw; /* Accumulated number of task switches */ + unsigned long jiffies; /* Track jiffies value */ +}; + /* Per-CPU data for read-copy update. */ struct rcu_data { /* 1) quiescent-state and grace-period handling : */ @@ -251,6 +268,8 @@ struct rcu_data { unsigned long rcu_onl_gp_seq; /* ->gp_seq at last online. */ short rcu_onl_gp_flags; /* ->gp_flags at last online. */ unsigned long last_fqs_resched; /* Time of last rcu_resched(). */ + struct rcu_snap_record snap_record; /* Snapshot of core stats at half of */ + /* the first RCU stall timeout */
int cpu; }; diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 338d35fc674a941..945b7de36a76d6d 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -395,6 +395,35 @@ static bool rcu_is_gp_kthread_starving(unsigned long *jp) return j > 2 * HZ; }
+static void print_cpu_stat_info(int cpu) +{ + struct rcu_snap_record rsr, *rsrp; + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + struct kernel_cpustat *kcsp = &kcpustat_cpu(cpu); + + if (!rcu_cpu_stall_cputime) + return; + + rsrp = &rdp->snap_record; + if (rsrp->gp_seq != rdp->gp_seq) + return; + + rsr.cputime_irq = kcpustat_field(kcsp, CPUTIME_IRQ, cpu); + rsr.cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu); + rsr.cputime_system = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu); + + pr_err("\t hardirqs softirqs csw/system\n"); + pr_err("\t number: %8ld %10d %12lld\n", + kstat_cpu_irqs_sum(cpu) - rsrp->nr_hardirqs, + kstat_cpu_softirqs_sum(cpu) - rsrp->nr_softirqs, + nr_context_switches_cpu(cpu) - rsrp->nr_csw); + pr_err("\tcputime: %8lld %10lld %12lld ==> %d(ms)\n", + div_u64(rsr.cputime_irq - rsrp->cputime_irq, NSEC_PER_MSEC), + div_u64(rsr.cputime_softirq - rsrp->cputime_softirq, NSEC_PER_MSEC), + div_u64(rsr.cputime_system - rsrp->cputime_system, NSEC_PER_MSEC), + jiffies_to_msecs(jiffies - rsrp->jiffies)); +} + /* * Print out diagnostic information for the specified stalled CPU. * @@ -447,6 +476,8 @@ static void print_cpu_stall_info(int cpu) data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart, fast_no_hz, falsepositive ? " (false positive?)" : ""); + + print_cpu_stat_info(cpu); }
/* Complain about starvation of grace-period kthread. */ diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 849f0aa99333bd8..0e3821783796522 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -497,6 +497,8 @@ EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress); module_param(rcu_cpu_stall_suppress, int, 0644); int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; module_param(rcu_cpu_stall_timeout, int, 0644); +int rcu_cpu_stall_cputime __read_mostly = IS_ENABLED(CONFIG_RCU_CPU_STALL_CPUTIME); +module_param(rcu_cpu_stall_cputime, int, 0644); #endif /* #ifdef CONFIG_RCU_STALL_COMMON */
// Suppress boot-time RCU CPU stall warnings and rcutorture writer stall