linux-kernel - [RFC PATCH 0/2] tiny_rcu: simplify tiny

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Date:	Fri, 28 Nov 2014 17:43:31 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	<linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
CC:	Lai Jiangshan <laijs@...fujitsu.com>,
	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [RFC PATCH 0/2] tiny_rcu: simplify tiny_rcu

Hi, Paul

These two patches use the special feture of the UP system:
	In UP, quiescent state == grace period.

For rcu_bh, rcu_process_callbacks() == a bh == QS == GP
so we can pass rcu_bh-QS and advance GP(and callbacks) in
rcu_process_callbacks(). After doing so, rcu_bh_qs() is useless
since its work is handled by rcu_process_callbacks().

For rcu_sched, context-switch = QS = GP, thus we can force a
context-switch when call_rcu_sched() is happened on idle_task.
After doing so, rcu_idle/irq_enter/exit() are useless.

These patches remove the useless code to simplify the tiny_rcu.

We can change rcu_bh_qs() rcu_idle/irq_enter/exit() to static-inline-functions
to reduce the binary size after these two patches accepted.

Thanks,
Lai

Cc: Josh Triplett <josh@...htriplett.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Lai Jiangshan (2):
  record rcu_bh quiescent state in RCU_SOFTIRQ
  tiny_rcu: resched when call_rcu() on idle_task

 kernel/rcu/rcu.h         |    6 ++
 kernel/rcu/tiny.c        |  134 ++++++++--------------------------------------
 kernel/rcu/tiny_plugin.h |    2 +-
 kernel/rcu/tree.c        |    6 --
 4 files changed, 29 insertions(+), 119 deletions(-)

-- 
1.7.4.4

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