diff options
| author | Frederic Weisbecker <frederic@kernel.org> | 2024-04-25 17:18:34 +0300 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2024-06-04 03:26:26 +0300 |
| commit | 483d5bf23125a9127ffcb3f7a3b3539b34df67d4 (patch) | |
| tree | 94be520b90e9225dbd8eae3a4c18b80d1e7b5d35 /include | |
| parent | aa97b9a56906f5965a7c5752790d174cadc8b820 (diff) | |
| download | linux-483d5bf23125a9127ffcb3f7a3b3539b34df67d4.tar.xz | |
rcu/nocb: Use kthread parking instead of ad-hoc implementation
Upon NOCB deoffloading, the rcuo kthread must be forced to sleep
until the corresponding rdp is ever offloaded again. The deoffloader
clears the SEGCBLIST_OFFLOADED flag, wakes up the rcuo kthread which
then notices that change and clears in turn its SEGCBLIST_KTHREAD_CB
flag before going to sleep, until it ever sees the SEGCBLIST_OFFLOADED
flag again, should a re-offloading happen.
Upon NOCB offloading, the rcuo kthread must be forced to wake up and
handle callbacks until the corresponding rdp is ever deoffloaded again.
The offloader sets the SEGCBLIST_OFFLOADED flag, wakes up the rcuo
kthread which then notices that change and sets in turn its
SEGCBLIST_KTHREAD_CB flag before going to check callbacks, until it
ever sees the SEGCBLIST_OFFLOADED flag cleared again, should a
de-offloading happen again.
This is all a crude ad-hoc and error-prone kthread (un-)parking
re-implementation.
Consolidate the behaviour with the appropriate API instead.
[ paulmck: Apply Qiang Zhang feedback provided in Link: below. ]
Link: https://lore.kernel.org/all/20240509074046.15629-1-qiang.zhang1211@gmail.com/
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/rcu_segcblist.h | 81 |
1 files changed, 36 insertions, 45 deletions
diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h index 8018045989af..ba95c06675e1 100644 --- a/include/linux/rcu_segcblist.h +++ b/include/linux/rcu_segcblist.h @@ -84,31 +84,31 @@ struct rcu_cblist { * ---------------------------------------------------------------------------- * | * v - * ----------------------------------- - * | | - * v v - * --------------------------------------- ----------------------------------| - * | SEGCBLIST_RCU_CORE | | | SEGCBLIST_RCU_CORE | | - * | SEGCBLIST_LOCKING | | | SEGCBLIST_LOCKING | | - * | SEGCBLIST_OFFLOADED | | | SEGCBLIST_OFFLOADED | | - * | SEGCBLIST_KTHREAD_CB | | SEGCBLIST_KTHREAD_GP | - * | | | | - * | | | | - * | CB kthread woke up and | | GP kthread woke up and | - * | acknowledged SEGCBLIST_OFFLOADED. | | acknowledged SEGCBLIST_OFFLOADED| - * | Processes callbacks concurrently | | | - * | with rcu_core(), holding | | | - * | nocb_lock. | | | - * --------------------------------------- ----------------------------------- - * | | - * ----------------------------------- + * ---------------------------------------------------------------------------- + * | SEGCBLIST_RCU_CORE | SEGCBLIST_LOCKING | SEGCBLIST_OFFLOADED | + * | + unparked CB kthread | + * | | + * | CB kthread got unparked and processes callbacks concurrently with | + * | rcu_core(), holding nocb_lock. | + * --------------------------------------------------------------------------- + * | + * v + * ---------------------------------------------------------------------------| + * | SEGCBLIST_RCU_CORE | | + * | SEGCBLIST_LOCKING | | + * | SEGCBLIST_OFFLOADED | | + * | SEGCBLIST_KTHREAD_GP | + * | + unparked CB kthread | + * | | + * | GP kthread woke up and acknowledged nocb_lock. | + * ---------------------------------------- ----------------------------------- * | * v * |--------------------------------------------------------------------------| - * | SEGCBLIST_LOCKING | | - * | SEGCBLIST_OFFLOADED | | + * | SEGCBLIST_LOCKING | | + * | SEGCBLIST_OFFLOADED | | * | SEGCBLIST_KTHREAD_GP | | - * | SEGCBLIST_KTHREAD_CB | + * | + unparked CB kthread | * | | * | Kthreads handle callbacks holding nocb_lock, local rcu_core() stops | * | handling callbacks. Enable bypass queueing. | @@ -124,8 +124,8 @@ struct rcu_cblist { * |--------------------------------------------------------------------------| * | SEGCBLIST_LOCKING | | * | SEGCBLIST_OFFLOADED | | - * | SEGCBLIST_KTHREAD_CB | | * | SEGCBLIST_KTHREAD_GP | + * | + unparked CB kthread | * | | * | CB/GP kthreads handle callbacks holding nocb_lock, local rcu_core() | * | ignores callbacks. Bypass enqueue is enabled. | @@ -136,8 +136,8 @@ struct rcu_cblist { * | SEGCBLIST_RCU_CORE | | * | SEGCBLIST_LOCKING | | * | SEGCBLIST_OFFLOADED | | - * | SEGCBLIST_KTHREAD_CB | | * | SEGCBLIST_KTHREAD_GP | + * | + unparked CB kthread | * | | * | CB/GP kthreads handle callbacks holding nocb_lock, local rcu_core() | * | handles callbacks concurrently. Bypass enqueue is disabled. | @@ -149,40 +149,31 @@ struct rcu_cblist { * |--------------------------------------------------------------------------| * | SEGCBLIST_RCU_CORE | | * | SEGCBLIST_LOCKING | | - * | SEGCBLIST_KTHREAD_CB | | * | SEGCBLIST_KTHREAD_GP | + * | + unparked CB kthread | * | | * | CB/GP kthreads and local rcu_core() handle callbacks concurrently | - * | holding nocb_lock. Wake up CB and GP kthreads if necessary. | + * | holding nocb_lock. Wake up GP kthread if necessary. | * ---------------------------------------------------------------------------- * | * v - * ----------------------------------- - * | | - * v v - * ---------------------------------------------------------------------------| - * | | | - * | SEGCBLIST_RCU_CORE | | SEGCBLIST_RCU_CORE | | - * | SEGCBLIST_LOCKING | | SEGCBLIST_LOCKING | | - * | SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP | - * | | | - * | GP kthread woke up and | CB kthread woke up and | - * | acknowledged the fact that | acknowledged the fact that | - * | SEGCBLIST_OFFLOADED got cleared. | SEGCBLIST_OFFLOADED got cleared. | - * | | The CB kthread goes to sleep | - * | The callbacks from the target CPU | until it ever gets re-offloaded. | - * | will be ignored from the GP kthread | | - * | loop. | | + * |--------------------------------------------------------------------------| + * | SEGCBLIST_RCU_CORE | | + * | SEGCBLIST_LOCKING | | + * | + unparked CB kthread | + * | | + * | GP kthread woke up and acknowledged the fact that SEGCBLIST_OFFLOADED | + * | got cleared. The callbacks from the target CPU will be ignored from the| + * | GP kthread loop. | * ---------------------------------------------------------------------------- - * | | - * ----------------------------------- * | * v * ---------------------------------------------------------------------------- * | SEGCBLIST_RCU_CORE | SEGCBLIST_LOCKING | + * | + parked CB kthread | * | | - * | Callbacks processed by rcu_core() from softirqs or local | - * | rcuc kthread, while holding nocb_lock. | + * | CB kthread is parked. Callbacks processed by rcu_core() from softirqs or | + * | local rcuc kthread, while holding nocb_lock. | * ---------------------------------------------------------------------------- * | * v |