From 8273ec1dbebbada22b8508082c533f90199df19c Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 9 Sep 2020 21:51:09 -0700 Subject: [PATCH] UPSTREAM: rcu-tasks: Selectively enable more RCU Tasks Trace IPIs Many workloads are quite sensitive to IPIs, and such workloads should build kernels with CONFIG_TASKS_TRACE_RCU_READ_MB=y to prevent RCU Tasks Trace from using them under normal conditions. However, other workloads are quite happy to permit more IPIs if doing so makes BPF program updates go faster. This commit therefore sets the default value for the rcupdate.rcu_task_ipi_delay kernel parameter to zero for kernels that have been built with CONFIG_TASKS_TRACE_RCU_READ_MB=n, while retaining the old default of (HZ / 10) for kernels that have indicated an aversion to IPIs via CONFIG_TASKS_TRACE_RCU_READ_MB=y. Link: https://lore.kernel.org/bpf/CAADnVQK_AiX+S_L_A4CQWT11XyveppBbQSQgH_qWGyzu_E8Yeg@mail.gmail.com/ Reported-by: Alexei Starovoitov Cc: Daniel Borkmann Cc: Jiri Olsa Cc: Change-Id: Ib139e578d1feb25c8f18aff0017fcb66138b06d1 Signed-off-by: Paul E. McKenney --- kernel/rcu/tasks.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index e8f0680968ca..07b1e5f96a16 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -68,7 +68,7 @@ static struct rcu_tasks rt_name = \ DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu); /* Avoid IPIing CPUs early in the grace period. */ -#define RCU_TASK_IPI_DELAY (HZ / 2) +#define RCU_TASK_IPI_DELAY (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) ? HZ / 2 : 0) static int rcu_task_ipi_delay __read_mostly = RCU_TASK_IPI_DELAY; module_param(rcu_task_ipi_delay, int, 0644); @@ -746,7 +746,8 @@ static void trc_wait_for_one_reader(struct task_struct *t, // If currently running, send an IPI, either way, add to list. trc_add_holdout(t, bhp); - if (task_curr(t) && time_after(jiffies, rcu_tasks_trace.gp_start + rcu_task_ipi_delay)) { + if (task_curr(t) && + time_after(jiffies + 1, rcu_tasks_trace.gp_start + rcu_task_ipi_delay)) { // The task is currently running, so try IPIing it. cpu = task_cpu(t);