rcuscale: Measure grace-period kthread CPU time

This commit adds the ability to output the CPU time consumed by the
grace-period kthread for the RCU variant under test.  The CPU time is
whatever is in the designated task's current->stime field, and thus is
controlled by whatever CPU-time accounting scheme is in effect.

This output appears in microseconds as follows on the console:

rcu_scale: Grace-period kthread CPU time: 42367.037

[ paulmck: Apply feedback from Stephen Rothwell and kernel test robot. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Yujie Liu <yujie.liu@intel.com>

diff --git a/include/linux/rcupdate_trace.h b/include/linux/rcupdate_trace.h
index 9bc8cbb33340b8ac2680c49f8ab65657eccd2077..eda493200663faf15780bff26c9ddc797afe9434 100644 (file)
--- a/include/linux/rcupdate_trace.h
+++ b/include/linux/rcupdate_trace.h
@@ -87,6 +87,7 @@ static inline void rcu_read_unlock_trace(void)
 void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
 void synchronize_rcu_tasks_trace(void);
 void rcu_barrier_tasks_trace(void);
+struct task_struct *get_rcu_tasks_trace_gp_kthread(void);
 #else
 /*
  * The BPF JIT forms these addresses even when it doesn't call these

diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index 821a3e65c54aec626967fe6de21336ccc0e1dfdb..7fba3ab66e35acdc8197f4199555ab755f382995 100644 (file)
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -141,6 +141,7 @@ struct rcu_scale_ops {
        void (*gp_barrier)(void);
        void (*sync)(void);
        void (*exp_sync)(void);
+       struct task_struct *(*rso_gp_kthread)(void);
        const char *name;
 };
 
@@ -336,6 +337,7 @@ static struct rcu_scale_ops tasks_tracing_ops = {
        .gp_barrier     = rcu_barrier_tasks_trace,
        .sync           = synchronize_rcu_tasks_trace,
        .exp_sync       = synchronize_rcu_tasks_trace,
+       .rso_gp_kthread = get_rcu_tasks_trace_gp_kthread,
        .name           = "tasks-tracing"
 };
 
@@ -563,6 +565,8 @@ static struct task_struct **kfree_reader_tasks;
 static int kfree_nrealthreads;
 static atomic_t n_kfree_scale_thread_started;
 static atomic_t n_kfree_scale_thread_ended;
+static struct task_struct *kthread_tp;
+static u64 kthread_stime;
 
 struct kfree_obj {
        char kfree_obj[8];
@@ -808,6 +812,18 @@ rcu_scale_cleanup(void)
        if (gp_exp && gp_async)
                SCALEOUT_ERRSTRING("No expedited async GPs, so went with async!");
 
+       // If built-in, just report all of the GP kthread's CPU time.
+       if (IS_BUILTIN(CONFIG_RCU_SCALE_TEST) && !kthread_tp && cur_ops->rso_gp_kthread)
+               kthread_tp = cur_ops->rso_gp_kthread();
+       if (kthread_tp) {
+               u32 ns;
+               u64 us;
+
+               kthread_stime = kthread_tp->stime - kthread_stime;
+               us = div_u64_rem(kthread_stime, 1000, &ns);
+               pr_info("rcu_scale: Grace-period kthread CPU time: %llu.%03u us\n", us, ns);
+               show_rcu_gp_kthreads();
+       }
        if (kfree_rcu_test) {
                kfree_scale_cleanup();
                return;
@@ -921,6 +937,11 @@ rcu_scale_init(void)
        if (cur_ops->init)
                cur_ops->init();
 
+       if (cur_ops->rso_gp_kthread) {
+               kthread_tp = cur_ops->rso_gp_kthread();
+               if (kthread_tp)
+                       kthread_stime = kthread_tp->stime;
+       }
        if (kfree_rcu_test)
                return kfree_scale_init();
 

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index b770add3f8430234110e0e3784a7108c94b06ef8..990a6cf5fa3511f935f3bddaade565654dee35ef 100644 (file)
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1830,6 +1830,12 @@ void show_rcu_tasks_trace_gp_kthread(void)
 EXPORT_SYMBOL_GPL(show_rcu_tasks_trace_gp_kthread);
 #endif // !defined(CONFIG_TINY_RCU)
 
+struct task_struct *get_rcu_tasks_trace_gp_kthread(void)
+{
+       return rcu_tasks_trace.kthread_ptr;
+}
+EXPORT_SYMBOL_GPL(get_rcu_tasks_trace_gp_kthread);
+
 #else /* #ifdef CONFIG_TASKS_TRACE_RCU */
 static void exit_tasks_rcu_finish_trace(struct task_struct *t) { }
 #endif /* #else #ifdef CONFIG_TASKS_TRACE_RCU */