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Commit 22607d66 authored by Paul E. McKenney's avatar Paul E. McKenney
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srcu: Specify auto-expedite holdoff time



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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: default avatarMike Galbraith <efault@gmx.de>
parent 2da4b2a7
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