Le Tue, Mar 19, 2024 at 02:54:57PM -0400, Joel Fernandes (Google) a écrit :
> In the synchronize_rcu() common case, we will have less than
> SR_MAX_USERS_WAKE_FROM_GP number of users per GP. Waking up the kworker
> is pointless just to free the last injected wait head since at that point,
> all the users have already been awakened.
>
> Introduce a new counter to track this and prevent the wakeup in the
> common case.
>
> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> ---
> v1->v2: Rebase on paul/dev
> v2->v3: Additional optimization for wait_tail->next == NULL case.
> v3->v4: Apply clean ups from Vlad. Tested rcutorture all scenarios.
> ---
> kernel/rcu/tree.c | 35 ++++++++++++++++++++++++++++++-----
> kernel/rcu/tree.h | 1 +
> 2 files changed, 31 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 9fbb5ab57c84..f3193670fe42 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -96,6 +96,7 @@ static struct rcu_state rcu_state = {
> .ofl_lock = __ARCH_SPIN_LOCK_UNLOCKED,
> .srs_cleanup_work = __WORK_INITIALIZER(rcu_state.srs_cleanup_work,
> rcu_sr_normal_gp_cleanup_work),
> + .srs_cleanups_pending = ATOMIC_INIT(0),
> };
>
> /* Dump rcu_node combining tree at boot to verify correct setup. */
> @@ -1642,8 +1643,11 @@ static void rcu_sr_normal_gp_cleanup_work(struct work_struct *work)
> * the done tail list manipulations are protected here.
> */
> done = smp_load_acquire(&rcu_state.srs_done_tail);
> - if (!done)
> + if (!done) {
Can this really happen? And if not should we warn?
> + /* See comments below. */
> + atomic_dec_return_release(&rcu_state.srs_cleanups_pending);
And if not should we really do that?
> return;
> + }
>
> WARN_ON_ONCE(!rcu_sr_is_wait_head(done));
> head = done->next;
> @@ -1666,6 +1670,9 @@ static void rcu_sr_normal_gp_cleanup_work(struct work_struct *work)
>
> rcu_sr_put_wait_head(rcu);
> }
> +
> + /* Order list manipulations with atomic access. */
> + atomic_dec_return_release(&rcu_state.srs_cleanups_pending);
Can we have a sanity check here ensuring this never goes negative?
Thanks.
