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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-01-25 07:24:14 +0100
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-02-26 20:57:28 +0100
commit89bf5d82ed451f02329bbbb06ac365e96b18804d (patch)
treeda9009ae1bf0bdb761ac2265b992bdc9c124fec4
parentdocumentation: Update rcutree.kthread_prio for grace-period kthread use (diff)
downloadlinux-89bf5d82ed451f02329bbbb06ac365e96b18804d.tar.xz
linux-89bf5d82ed451f02329bbbb06ac365e96b18804d.zip
documentation: Update based on on-demand vmstat workers
Now that the on-demand vmstat workers commit is in mainline, it is possible to eliminate vmstat_update()-induced OS jitter. This commit updates the documentation accordingly. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
-rw-r--r--Documentation/kernel-per-CPU-kthreads.txt18
1 files changed, 10 insertions, 8 deletions
diff --git a/Documentation/kernel-per-CPU-kthreads.txt b/Documentation/kernel-per-CPU-kthreads.txt
index f3cd299fcc41..81fe051c4447 100644
--- a/Documentation/kernel-per-CPU-kthreads.txt
+++ b/Documentation/kernel-per-CPU-kthreads.txt
@@ -190,14 +190,16 @@ To reduce its OS jitter, do any of the following:
on each CPU, including cs_dbs_timer() and od_dbs_timer().
WARNING: Please check your CPU specifications to
make sure that this is safe on your particular system.
- d. It is not possible to entirely get rid of OS jitter
- from vmstat_update() on CONFIG_SMP=y systems, but you
- can decrease its frequency by writing a large value
- to /proc/sys/vm/stat_interval. The default value is
- HZ, for an interval of one second. Of course, larger
- values will make your virtual-memory statistics update
- more slowly. Of course, you can also run your workload
- at a real-time priority, thus preempting vmstat_update(),
+ d. As of v3.18, Christoph Lameter's on-demand vmstat workers
+ commit prevents OS jitter due to vmstat_update() on
+ CONFIG_SMP=y systems. Before v3.18, is not possible
+ to entirely get rid of the OS jitter, but you can
+ decrease its frequency by writing a large value to
+ /proc/sys/vm/stat_interval. The default value is HZ,
+ for an interval of one second. Of course, larger values
+ will make your virtual-memory statistics update more
+ slowly. Of course, you can also run your workload at
+ a real-time priority, thus preempting vmstat_update(),
but if your workload is CPU-bound, this is a bad idea.
However, there is an RFC patch from Christoph Lameter
(based on an earlier one from Gilad Ben-Yossef) that