2022-11-21 15:50:20

by Zqiang

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

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 <[email protected]>
---
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

2022-11-22 01:41:37

by Paul E. McKenney

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 <[email protected]>

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
>