After enabling CONFIG_IRQ_TIME_ACCOUNTING to monitor IRQ pressure in our container environment, we observed several noticeable behavioral changes. One of our IRQ-heavy services, such as Redis, reported a significant reduction in CPU usage after upgrading to the new kernel with CONFIG_IRQ_TIME_ACCOUNTING enabled. However, despite adding more threads to handle an increased workload, the CPU usage could not be raised. In other words, even though the container’s CPU usage appeared low, it was unable to process more workloads to utilize additional CPU resources, which caused issues. This behavior can be demonstrated using netperf: function start_server() { for j in `seq 1 3`; do netserver -p $[12345+j] > /dev/null & done } server_ip=$1 function start_client() { # That applies to cgroup2 as well. mkdir -p /sys/fs/cgroup/cpuacct/test echo $$ > /sys/fs/cgroup/cpuacct/test/cgroup.procs for j in `seq 1 3`; do port=$[12345+j] taskset -c 0 netperf -H ${server_ip} -l ${run_time:-30000} \ -t TCP_STREAM -p $port -- -D -m 1k -M 1K -s 8k -S 8k \ > /dev/null & done } start_server start_client We can verify the CPU usage of the test cgroup using cpuacct.stat. The output shows: system: 53 user: 2 The CPU usage of the cgroup is relatively low at around 55%, but this usage doesn't increase, even with more netperf tasks. The reason is that CPU0 is at 100% utilization, as confirmed by mpstat: 02:56:22 PM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle 02:56:23 PM 0 0.99 0.00 55.45 0.00 0.99 42.57 0.00 0.00 0.00 0.00 02:56:23 PM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle 02:56:24 PM 0 2.00 0.00 55.00 0.00 0.00 43.00 0.00 0.00 0.00 0.00 It is clear that the %soft is not accounted into the cgroup of the interrupted task. This behavior is unexpected. We should account for IRQ time to the cgroup to reflect the pressure the group is under. After a thorough analysis, I discovered that this change in behavior is due to commit 305e6835e055 ("sched: Do not account irq time to current task"), which altered whether IRQ time should be charged to the interrupted task. While I agree that a task should not be penalized by random interrupts, the task itself cannot progress while interrupted. Therefore, the interrupted time should be reported to the user. The system metric in cpuacct.stat is crucial in indicating whether a container is under heavy system pressure, including IRQ/softirq activity. Hence, IRQ/softirq time should be accounted for in the cpuacct system usage, which also applies to cgroup2’s rstat. This patch reintroduces IRQ/softirq accounting to cgroups. Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> --- kernel/sched/core.c | 33 +++++++++++++++++++++++++++++++-- kernel/sched/psi.c | 14 +++----------- kernel/sched/stats.h | 7 ++++--- 3 files changed, 38 insertions(+), 16 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 06a06f0897c3..5ed2c5c8c911 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5579,6 +5579,35 @@ __setup("resched_latency_warn_ms=", setup_resched_latency_warn_ms); static inline u64 cpu_resched_latency(struct rq *rq) { return 0; } #endif /* CONFIG_SCHED_DEBUG */ +#ifdef CONFIG_IRQ_TIME_ACCOUNTING +static void account_irqtime(struct rq *rq, struct task_struct *curr, + struct task_struct *prev) +{ + int cpu = smp_processor_id(); + s64 delta; + u64 irq; + + if (!static_branch_likely(&sched_clock_irqtime)) + return; + + irq = irq_time_read(cpu); + delta = (s64)(irq - rq->psi_irq_time); + if (delta < 0) + return; + + rq->psi_irq_time = irq; + psi_account_irqtime(rq, curr, prev, delta); + cgroup_account_cputime(curr, delta); + /* We account both softirq and irq into softirq */ + cgroup_account_cputime_field(curr, CPUTIME_SOFTIRQ, delta); +} +#else +static inline void account_irqtime(struct rq *rq, struct task_struct *curr, + struct task_struct *prev) +{ +} +#endif + /* * This function gets called by the timer code, with HZ frequency. * We call it with interrupts disabled. @@ -5600,7 +5629,7 @@ void sched_tick(void) rq_lock(rq, &rf); curr = rq->curr; - psi_account_irqtime(rq, curr, NULL); + account_irqtime(rq, curr, NULL); update_rq_clock(rq); hw_pressure = arch_scale_hw_pressure(cpu_of(rq)); @@ -6683,7 +6712,7 @@ static void __sched notrace __schedule(int sched_mode) ++*switch_count; migrate_disable_switch(rq, prev); - psi_account_irqtime(rq, prev, next); + account_irqtime(rq, prev, next); psi_sched_switch(prev, next, block); trace_sched_switch(preempt, prev, next, prev_state); diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c index 4d26a106f03b..1adb41b2ae1d 100644 --- a/kernel/sched/psi.c +++ b/kernel/sched/psi.c @@ -990,16 +990,14 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next, } #ifdef CONFIG_IRQ_TIME_ACCOUNTING -void psi_account_irqtime(struct rq *rq, struct task_struct *curr, struct task_struct *prev) +void psi_account_irqtime(struct rq *rq, struct task_struct *curr, struct task_struct *prev, + s64 delta) { int cpu = task_cpu(curr); struct psi_group *group; struct psi_group_cpu *groupc; - s64 delta; - u64 irq; - if (static_branch_likely(&psi_disabled) || - !static_branch_likely(&sched_clock_irqtime)) + if (static_branch_likely(&psi_disabled)) return; if (!curr->pid) @@ -1010,12 +1008,6 @@ void psi_account_irqtime(struct rq *rq, struct task_struct *curr, struct task_st if (prev && task_psi_group(prev) == group) return; - irq = irq_time_read(cpu); - delta = (s64)(irq - rq->psi_irq_time); - if (delta < 0) - return; - rq->psi_irq_time = irq; - do { u64 now; diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h index 767e098a3bd1..17eefe5876a5 100644 --- a/kernel/sched/stats.h +++ b/kernel/sched/stats.h @@ -111,10 +111,11 @@ void psi_task_change(struct task_struct *task, int clear, int set); void psi_task_switch(struct task_struct *prev, struct task_struct *next, bool sleep); #ifdef CONFIG_IRQ_TIME_ACCOUNTING -void psi_account_irqtime(struct rq *rq, struct task_struct *curr, struct task_struct *prev); +void psi_account_irqtime(struct rq *rq, struct task_struct *curr, + struct task_struct *prev, s64 delta); #else static inline void psi_account_irqtime(struct rq *rq, struct task_struct *curr, - struct task_struct *prev) {} + struct task_struct *prev, s64 delta) {} #endif /*CONFIG_IRQ_TIME_ACCOUNTING */ /* * PSI tracks state that persists across sleeps, such as iowaits and @@ -215,7 +216,7 @@ static inline void psi_sched_switch(struct task_struct *prev, struct task_struct *next, bool sleep) {} static inline void psi_account_irqtime(struct rq *rq, struct task_struct *curr, - struct task_struct *prev) {} + struct task_struct *prev, s64 delta) {} #endif /* CONFIG_PSI */ #ifdef CONFIG_SCHED_INFO -- 2.43.5