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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-04-26 00:03:11 +0300
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-04-27 02:32:17 +0300
commit22607d66bbc3e81140d3bcf08894f4378eb36428 (patch)
tree88b0caa1cd8bfa66e6a4b00ad21108f03369eb03 /Documentation/admin-guide
parent2da4b2a7fd8de52c44fa83c59f00d38a0d90caae (diff)
downloadlinux-22607d66bbc3e81140d3bcf08894f4378eb36428.tar.xz
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: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Mike Galbraith <efault@gmx.de>
Diffstat (limited to 'Documentation/admin-guide')
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt8
1 files changed, 8 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index facc20a3f962..4a4b9266c4de 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3779,6 +3779,14 @@
spia_pedr=
spia_peddr=
+ srcutree.exp_holdoff [KNL]
+ Specifies how many nanoseconds must elapse
+ since the end of the last SRCU grace period for
+ a given srcu_struct until the next normal SRCU
+ grace period will be considered for automatic
+ expediting. Set to zero to disable automatic
+ expediting.
+
stacktrace [FTRACE]
Enabled the stack tracer on boot up.