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

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Date:   Mon, 21 Nov 2022 17:30:19 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Zqiang <qiang1.zhang@...el.com>
Cc:     frederic@...nel.org, joel@...lfernandes.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu-tasks: Use accurate runstart time for RCU Tasks
 boot-time testing

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@...el.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
>