Le Wed, Oct 09, 2024 at 06:21:24PM +0530, neeraj.upadh...@kernel.org a écrit :
> From: Neeraj Upadhyay <neeraj.upadh...@kernel.org>
>
> Use RCU watching state of a CPU to check whether RCU-tasks GP
> need to wait for idle injection task on that CPU. Idle injection
> tasks which are in deep-idle states where RCU is not watching or
> which have transitioned to/from deep-idle state do not block
> RCU-tasks grace period.
>
> Signed-off-by: Neeraj Upadhyay <neeraj.upadh...@kernel.org>
For now this should work because there is a single user that is
a per-cpu kthread, therefore no RCU-watching writer can race
against another (real idle VS idle injection or idle_injection VS
idle injection) without going first through a voluntary context
switch. But who knows about the future? If an idle injection kthread
is preempted by another idle injection right after clearing PF_IDLE,
there could be some spurious QS accounted for the preempted
kthread.
So perhaps we can consider idle injection as any normal task and
wait for it to voluntary schedule?
Well I see DEFAULT_DURATION_JIFFIES = 6, which is 60 ms on HZ=100.
Yeah that's a lot...so perhaps this patch is needed after all...
> ---
> kernel/rcu/tasks.h | 63 +++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 48 insertions(+), 15 deletions(-)
>
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index d8506d2e6f54..1947f9b6346d 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -38,6 +38,8 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp);
> * @rtpp: Pointer to the rcu_tasks structure.
> * @rcu_watching_snap: Per-GP RCU-watching snapshot for idle tasks.
> * @rcu_watching_snap_rec: RCU-watching snapshot recorded for idle task.
> + * @rcu_watching_idle_inj_snap: Per-GP RCU-watching snapshot for idle inject
> task.
> + * @rcu_watching_idle_inj_rec: RCU-watching snapshot recorded for idle
> inject task.
> */
> struct rcu_tasks_percpu {
> struct rcu_segcblist cblist;
> @@ -56,6 +58,8 @@ struct rcu_tasks_percpu {
> struct rcu_tasks *rtpp;
> int rcu_watching_snap;
> bool rcu_watching_snap_rec;
> + int rcu_watching_idle_inj_snap;
> + bool rcu_watching_idle_inj_rec;
So how about:
struct rcu_watching_task {
int snap;
bool rec;
}
...
struct rcu_tasks_percpu {
...
struct rcu_watching_task idle_task;
struct rcu_watching_task idle_inject;
}
Thanks.
