lk/linux-kernel-test
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

rcu: Merge preemptable-RCU functionality into hierarchical RCU

Browse Source 
Create a kernel/rcutree_plugin.h file that contains definitions
for preemptable RCU (or, under the #else branch of the #ifdef,
empty definitions for the classic non-preemptable semantics).
These definitions fit into plugins defined in kernel/rcutree.c
for this purpose.

This variant of preemptable RCU uses a new algorithm whose
read-side expense is roughly that of classic hierarchical RCU
under CONFIG_PREEMPT. This new algorithm's update-side expense
is similar to that of classic hierarchical RCU, and, in absence
of read-side preemption or blocking, is exactly that of classic
hierarchical RCU.  Perhaps more important, this new algorithm
has a much simpler implementation, saving well over 1,000 lines
of code compared to mainline's implementation of preemptable
RCU, which will hopefully be retired in favor of this new
algorithm.

The simplifications are obtained by maintaining per-task
nesting state for running tasks, and using a simple
lock-protected algorithm to handle accounting when tasks block
within RCU read-side critical sections, making use of lessons
learned while creating numerous user-level RCU implementations
over the past 18 months.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josht@linux.vnet.ibm.com
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
LKML-Reference: <12509746134003-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Paul E. McKenney
2009-08-22 13:56:52 -07:00
committed by Ingo Molnar
parent a157229cab
commit f41d911f8c
14 changed files with 662 additions and 56 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
init/Kconfig
View File

@@ -335,11 +335,20 @@ config PREEMPT_RCU
now-naive assumptions about each RCU read-side critical section
remaining on a given CPU through its execution.
config TREE_PREEMPT_RCU
bool "Preemptable tree-based hierarchical RCU"
depends on PREEMPT
help
This option selects the RCU implementation that is
designed for very large SMP systems with hundreds or
thousands of CPUs, but for which real-time response
is also required.
endchoice
config RCU_TRACE
bool "Enable tracing for RCU"
depends on TREE_RCU || PREEMPT_RCU
depends on TREE_RCU || PREEMPT_RCU || TREE_PREEMPT_RCU
help
This option provides tracing in RCU which presents stats
in debugfs for debugging RCU implementation.
@@ -351,7 +360,7 @@ config RCU_FANOUT
int "Tree-based hierarchical RCU fanout value"
range 2 64 if 64BIT
range 2 32 if !64BIT
depends on TREE_RCU
depends on TREE_RCU || TREE_PREEMPT_RCU
default 64 if 64BIT
default 32 if !64BIT
help
@@ -366,7 +375,7 @@ config RCU_FANOUT
config RCU_FANOUT_EXACT
bool "Disable tree-based hierarchical RCU auto-balancing"
depends on TREE_RCU
depends on TREE_RCU || TREE_PREEMPT_RCU
default n
help
This option forces use of the exact RCU_FANOUT value specified,
@@ -379,11 +388,12 @@ config RCU_FANOUT_EXACT
Say N if unsure.
config TREE_RCU_TRACE
def_bool RCU_TRACE && TREE_RCU
def_bool RCU_TRACE && ( TREE_RCU || TREE_PREEMPT_RCU )
select DEBUG_FS
help
This option provides tracing for the TREE_RCU implementation,
permitting Makefile to trivially select kernel/rcutree_trace.c.
This option provides tracing for the TREE_RCU and
TREE_PREEMPT_RCU implementations, permitting Makefile to
trivially select kernel/rcutree_trace.c.
config PREEMPT_RCU_TRACE
def_bool RCU_TRACE && PREEMPT_RCU