On Mon, Jan 09, 2023 at 10:17:56PM +0000, Joel Fernandes (Google) wrote:
> During suspend, we see failures to suspend 1 in 300-500 suspends.
> Looking closer, it appears that we are queuing lazy callbacks even
> though rcu_gp_is_expedited(). These delays appear to not be very welcome
> by the suspend/resume code as evidenced by these occasional suspend
> failures.
>
> This commit therefore checks if rcu_gp_is_expedited() and ignores the
> lazy hint if so.
>
> Ignoring the lazy hint if rcu_gp_is_expedited() makes the 3000
> suspend/resume cycles pass reliably on a 12th gen 12-core Intel CPU.
Yow!!! ;-)
> Fixes: 3cb278e73be5 ("rcu: Make call_rcu() lazy to save power")
> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> ---
> Paul, could we take this for 6.2 -rc cycle? Thanks.
>
> kernel/rcu/tree.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 63545d79da51..93eb03f8ed99 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2594,12 +2594,12 @@ static void check_cb_ovld(struct rcu_data *rdp)
> }
>
> static void
> -__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy)
> +__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
> {
> static atomic_t doublefrees;
> unsigned long flags;
> struct rcu_data *rdp;
> - bool was_alldone;
> + bool was_alldone, lazy;
Please put "lazy" in alpha order. Except that...
> /* Misaligned rcu_head! */
> WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
> @@ -2622,6 +2622,7 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy)
> kasan_record_aux_stack_noalloc(head);
> local_irq_save(flags);
> rdp = this_cpu_ptr(&rcu_data);
> + lazy = lazy_in && !rcu_gp_is_expedited();
Doesn't this completely disable laziness on Android?
Thanx, Paul
> /* Add the callback to our list. */
> if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
> --
> 2.39.0.314.g84b9a713c41-goog
