From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> The various RCU tasks flavors currently wait 100 milliseconds between each grace period in order to prevent CPU-bound loops and to favor efficiency over latency. However, RCU Tasks Trace needs to have a grace-period latency of roughly 25 milliseconds, which is completely infeasible given the 100-millisecond per-grace-period sleep. This commit therefore reduces this sleep duration to 5 milliseconds (or one jiffy, whichever is longer) in kernels built with CONFIG_TASKS_TRACE_RCU_READ_MB=y. Link: https://lore.kernel.org/bpf/CAADnVQK_AiX+S_L_A4CQWT11XyveppBbQSQgH_qWGyzu_E8Yeg@xxxxxxxxxxxxxx/ Reported-by: Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Cc: Jiri Olsa <jolsa@xxxxxxxxxx> Cc: <bpf@xxxxxxxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- kernel/rcu/tasks.h | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 2b4df23..a0eaed5 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -28,6 +28,7 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp); * @kthread_ptr: This flavor's grace-period/callback-invocation kthread. * @gp_func: This flavor's grace-period-wait function. * @gp_state: Grace period's most recent state transition (debugging). + * @gp_sleep: Per-grace-period sleep to prevent CPU-bound looping. * @init_fract: Initial backoff sleep interval. * @gp_jiffies: Time of last @gp_state transition. * @gp_start: Most recent grace-period start in jiffies. @@ -49,6 +50,7 @@ struct rcu_tasks { struct wait_queue_head cbs_wq; raw_spinlock_t cbs_lock; int gp_state; + int gp_sleep; int init_fract; unsigned long gp_jiffies; unsigned long gp_start; @@ -233,7 +235,7 @@ static int __noreturn rcu_tasks_kthread(void *arg) cond_resched(); } /* Paranoid sleep to keep this from entering a tight loop */ - schedule_timeout_idle(HZ/10); + schedule_timeout_idle(rtp->gp_sleep); set_tasks_gp_state(rtp, RTGS_WAIT_CBS); } @@ -557,6 +559,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks); static int __init rcu_spawn_tasks_kthread(void) { + rcu_tasks.gp_sleep = HZ / 10; rcu_tasks.init_fract = 10; rcu_tasks.pregp_func = rcu_tasks_pregp_step; rcu_tasks.pertask_func = rcu_tasks_pertask; @@ -690,6 +693,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks_rude); static int __init rcu_spawn_tasks_rude_kthread(void) { + rcu_tasks_rude.gp_sleep = HZ / 10; rcu_spawn_tasks_kthread_generic(&rcu_tasks_rude); return 0; } @@ -1170,8 +1174,12 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks_trace); static int __init rcu_spawn_tasks_trace_kthread(void) { if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) { + rcu_tasks_trace.gp_sleep = HZ / 10; rcu_tasks_trace.init_fract = 10; } else { + rcu_tasks_trace.gp_sleep = HZ / 200; + if (rcu_tasks_trace.gp_sleep <= 0) + rcu_tasks_trace.gp_sleep = 1; rcu_tasks_trace.init_fract = HZ / 5; if (rcu_tasks_trace.init_fract <= 0) rcu_tasks_trace.init_fract = 1; -- 2.9.5
