srcu: Specify auto-expedite holdoff time

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On small systems, in the absence of readers, expedited SRCU grace
periods can complete in less than a microsecond.  This means that an
eight-CPU system can have all CPUs doing synchronize_srcu() in a tight
loop and almost always expedite.  This might actually be desirable in
some situations, but in general it is a good way to needlessly burn
CPU cycles.  And in those situations where it is desirable, your friend
is the function synchronize_srcu_expedited().

For other situations, this commit adds a kernel parameter that specifies
a holdoff between completing the last SRCU grace period and auto-expediting
the next.  If the next grace period starts before the holdoff expires,
auto-expediting is disabled.  The holdoff is 50 microseconds by default,
and can be tuned to the desired number of nanoseconds.  A value of zero
disables auto-expediting.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Mike Galbraith <efault@gmx.de>

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This commit is contained in:

Paul E. McKenney 2017-04-25 14:03:11 -07:00

parent 2da4b2a7fd

commit 22607d66bb

3 changed files with 26 additions and 1 deletions

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8

Documentation/admin-guide/kernel-parameters.txt

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1

include/linux/srcutree.h

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18

kernel/rcu/srcutree.c

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