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| author | Paul E. McKenney <paulmck@kernel.org> | 2019-10-30 21:56:10 +0300 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2020-02-21 03:00:20 +0300 |
| commit | b2b00ddf193bf83dc561d965c67b18eb54ebcd83 (patch) | |
| tree | 0cd4acf7fe8ab47afc17067de5bbde675a6d1dd3 /Documentation/admin-guide | |
| parent | b5ea03709d12e98fa341aecfa6940cc9f49e8817 (diff) | |
| download | linux-b2b00ddf193bf83dc561d965c67b18eb54ebcd83.tar.xz | |
rcu: React to callback overload by aggressively seeking quiescent states
In default configutions, RCU currently waits at least 100 milliseconds
before asking cond_resched() and/or resched_rcu() for help seeking
quiescent states to end a grace period. But 100 milliseconds can be
one good long time during an RCU callback flood, for example, as can
happen when user processes repeatedly open and close files in a tight
loop. These 100-millisecond gaps in successive grace periods during a
callback flood can result in excessive numbers of callbacks piling up,
unnecessarily increasing memory footprint.
This commit therefore asks cond_resched() and/or resched_rcu() for help
as early as the first FQS scan when at least one of the CPUs has more
than 20,000 callbacks queued, a number that can be changed using the new
rcutree.qovld kernel boot parameter. An auxiliary qovld_calc variable
is used to avoid acquisition of locks that have not yet been initialized.
Early tests indicate that this reduces the RCU-callback memory footprint
during rcutorture floods by from 50% to 4x, depending on configuration.
Reported-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Reported-by: Tejun Heo <tj@kernel.org>
[ paulmck: Fix bug located by Qian Cai. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Dexuan Cui <decui@microsoft.com>
Tested-by: Qian Cai <cai@lca.pw>
Diffstat (limited to 'Documentation/admin-guide')
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index dbc22d684627..dbd4b4a65209 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3980,6 +3980,15 @@ Set threshold of queued RCU callbacks below which batch limiting is re-enabled. + rcutree.qovld= [KNL] + Set threshold of queued RCU callbacks beyond which + RCU's force-quiescent-state scan will aggressively + enlist help from cond_resched() and sched IPIs to + help CPUs more quickly reach quiescent states. + Set to less than zero to make this be set based + on rcutree.qhimark at boot time and to zero to + disable more aggressive help enlistment. + rcutree.rcu_idle_gp_delay= [KNL] Set wakeup interval for idle CPUs that have RCU callbacks (RCU_FAST_NO_HZ=y). |