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The rcupdate.rcu_task_enqueue_lim module parameter allows system administrators to tune the number of callback queues used by the RCU Tasks flavors. However if callback storms are infrequent, it would be better to operate with a single queue on a given system unless and until that system actually needed more queues. Systems not needing more queues can then avoid the overhead of checking the extra queues and especially avoid the overhead of fanning workqueue handlers out to all CPUs to invoke callbacks. This commit therefore switches to using all the CPUs' callback queues if call_rcu_tasks_generic() encounters too much lock contention. The amount of lock contention to tolerate defaults to 100 contended lock acquisitions per jiffy, and can be adjusted using the new rcupdate.rcu_task_contend_lim module parameter. Such switching is undertaken only if the rcupdate.rcu_task_enqueue_lim module parameter is negative, which is its default value (-1). This allows savvy systems administrators to set the number of queues to some known good value and to not have to worry about the kernel doing any second guessing. [ paulmck: Apply feedback from Guillaume Tucker and kernelci. ] Reported-by: Martin Lau <kafai@fb.com> Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> |
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| .. | ||
| Kconfig | ||
| Kconfig.debug | ||
| Makefile | ||
| rcu_segcblist.c | ||
| rcu_segcblist.h | ||
| rcu.h | ||
| rcuscale.c | ||
| rcutorture.c | ||
| refscale.c | ||
| srcutiny.c | ||
| srcutree.c | ||
| sync.c | ||
| tasks.h | ||
| tiny.c | ||
| tree_exp.h | ||
| tree_nocb.h | ||
| tree_plugin.h | ||
| tree_stall.h | ||
| tree.c | ||
| tree.h | ||
| update.c | ||