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UPSTREAM: rcu: Fix late wakeup when flush of bypass cblist happens

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When the bypass cblist gets too big or its timeout has occurred, it is
flushed into the main cblist. However, the bypass timer is still running
and the behavior is that it would eventually expire and wake the GP
thread.

Since we are going to use the bypass cblist for lazy CBs, do the wakeup
soon as the flush for "too big or too long" bypass list happens.
Otherwise, long delays can happen for callbacks which get promoted from
lazy to non-lazy.

This is a good thing to do anyway (regardless of future lazy patches),
since it makes the behavior consistent with behavior of other code paths
where flushing into the ->cblist makes the GP kthread into a
non-sleeping state quickly.

[ Frederic Weisbecker: Changes to avoid unnecessary GP-thread wakeups plus
		    comment changes. ]

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
(cherry picked from commit b50606f35f)

Bug: 258241771
Bug: 222463781
Test: powerIdle lab tests.
Change-Id: If8da96d7ba6ed90a2a70f7d56f7bb03af44fd649
Signed-off-by: Joel Fernandes <joelaf@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/4065239
Reviewed-by: Vineeth Pillai <vineethrp@google.com>
(cherry picked from commit 75db04e1eed1756a4ee5fb87ef8dd494d19bf53f)
[Cherry picked from chromeos-5.15 tree. Minor tweaks to commit message
to match Android style]
Signed-off-by: Qais Yousef <qyousef@google.com>
This commit is contained in:
Joel Fernandes (Google)
2022-09-17 16:41:59 +00:00
committed by Treehugger Robot
parent 24e6758060
commit 276d33f21a
1 changed files with 8 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
kernel/rcu/tree_nocb.h
View File

@@ -438,8 +438,9 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) ||
ncbs >= qhimark) {
rcu_nocb_lock(rdp);
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
if (!rcu_nocb_flush_bypass(rdp, rhp, j)) {
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
if (*was_alldone)
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("FirstQ"));
@@ -452,7 +453,12 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
rcu_advance_cbs_nowake(rdp->mynode, rdp);
rdp->nocb_gp_adv_time = j;
}
rcu_nocb_unlock_irqrestore(rdp, flags);
// The flush succeeded and we moved CBs into the regular list.
// Don't wait for the wake up timer as it may be too far ahead.
// Wake up the GP thread now instead, if the cblist was empty.
__call_rcu_nocb_wake(rdp, *was_alldone, flags);
return true; // Callback already enqueued.
}