linux-kernel - [PATCH RFC tip/core/rcu 0/5] Expedited grace periods encouraging normal ones

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Message-ID: <20150630214805.GA7795@linux.vnet.ibm.com>
Date:	Tue, 30 Jun 2015 14:48:05 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	bobby.prani@...il.com
Subject: [PATCH RFC tip/core/rcu 0/5] Expedited grace periods encouraging
 normal ones

Hello!

This series contains some highly experimental patches that allow normal
grace periods to take advantage of the work done by concurrent expedited
grace periods.  This can reduce the overhead incurred by normal grace
periods by eliminating the need for force-quiescent-state scans that
would otherwise have happened after the expedited grace period completed.
It is not clear whether this is a useful tradeoff.  Nevertheless, this
series contains the following patches:

1.	Pure code-movement commit that allows the RCU grace-period kthread
	to access the expedited grace period's state.

2.	Use snapshot technique to allow a normal grace period to complete
	after an expedited grace period has completed.

3.	Changes to rcutorture to fully test normal grace periods.  Current
	tests would fail to notice some types of forward-progress bugs due
	to the presence of expedited grace periods in the common case.

4.	Make expedited grace periods awaken any concurrent normal grace
	periods.

5.	Throttle the awakening to avoid excessive CPU consumption by the
	normal grace-period kthread.

A separate series will cover changes to the expedited grace-period
machinery itself.

							Thanx, Paul

------------------------------------------------------------------------

 b/kernel/rcu/rcutorture.c |   22 +++++-
 b/kernel/rcu/tree.c       |  165 +++++++++++++++++++++++++++-------------------
 b/kernel/rcu/tree.h       |    6 +
 3 files changed, 127 insertions(+), 66 deletions(-)

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