[PATCH] rcu-tasks: Use accurate runstart time for RCU Tasks boot-time testing

[PATCH] rcu-tasks: Use accurate runstart time for RCU Tasks boot-time testing

[Zqiang]

Currently, only get jiffies once as the runstart time for all RCU
Tasks testing. it's not accurate, for each RCU Tasks type test, since
corresponding type of synchronize_rcu_tasks*() be invoked, so before
each RCU Tasks test starts, we need to wait for the grace period of
the previous RCU Tasks test to end, there will be a deviation in the
start time of the RCU Tasks test.

Therefore, this commit at the start of each RCU Tasks test, re-fetch the
jiffies time as the runstart time.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
---
 kernel/rcu/tasks.h | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index b0b885e071fa..4a991311be9b 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1813,23 +1813,21 @@ static void test_rcu_tasks_callback(struct rcu_head *rhp)
 
 static void rcu_tasks_initiate_self_tests(void)
 {
-	unsigned long j = jiffies;
-
 	pr_info("Running RCU-tasks wait API self tests\n");
 #ifdef CONFIG_TASKS_RCU
-	tests[0].runstart = j;
+	tests[0].runstart = jiffies;
 	synchronize_rcu_tasks();
 	call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback);
 #endif
 
 #ifdef CONFIG_TASKS_RUDE_RCU
-	tests[1].runstart = j;
+	tests[1].runstart = jiffies;
 	synchronize_rcu_tasks_rude();
 	call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback);
 #endif
 
 #ifdef CONFIG_TASKS_TRACE_RCU
-	tests[2].runstart = j;
+	tests[2].runstart = jiffies;
 	synchronize_rcu_tasks_trace();
 	call_rcu_tasks_trace(&tests[2].rh, test_rcu_tasks_callback);
 #endif
-- 
2.25.1

Re: [PATCH] rcu-tasks: Use accurate runstart time for RCU Tasks boot-time testing

[Paul E. McKenney]

On Mon, Nov 21, 2022 at 11:01:50PM +0800, Zqiang wrote:
> Currently, only get jiffies once as the runstart time for all RCU
> Tasks testing. it's not accurate, for each RCU Tasks type test, since
> corresponding type of synchronize_rcu_tasks*() be invoked, so before
> each RCU Tasks test starts, we need to wait for the grace period of
> the previous RCU Tasks test to end, there will be a deviation in the
> start time of the RCU Tasks test.
> 
> Therefore, this commit at the start of each RCU Tasks test, re-fetch the
> jiffies time as the runstart time.
> 
> Signed-off-by: Zqiang <qiang1.zhang@intel.com>

Good catch!  Applied with the usual wordsmithing, so please do check.

							Thanx, Paul

> ---
>  kernel/rcu/tasks.h | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index b0b885e071fa..4a991311be9b 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -1813,23 +1813,21 @@ static void test_rcu_tasks_callback(struct rcu_head *rhp)
>  
>  static void rcu_tasks_initiate_self_tests(void)
>  {
> -	unsigned long j = jiffies;
> -
>  	pr_info("Running RCU-tasks wait API self tests\n");
>  #ifdef CONFIG_TASKS_RCU
> -	tests[0].runstart = j;
> +	tests[0].runstart = jiffies;
>  	synchronize_rcu_tasks();
>  	call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback);
>  #endif
>  
>  #ifdef CONFIG_TASKS_RUDE_RCU
> -	tests[1].runstart = j;
> +	tests[1].runstart = jiffies;
>  	synchronize_rcu_tasks_rude();
>  	call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback);
>  #endif
>  
>  #ifdef CONFIG_TASKS_TRACE_RCU
> -	tests[2].runstart = j;
> +	tests[2].runstart = jiffies;
>  	synchronize_rcu_tasks_trace();
>  	call_rcu_tasks_trace(&tests[2].rh, test_rcu_tasks_callback);
>  #endif
> -- 
> 2.25.1
>