[PATCH tip/core/rcu 4/6] documentation: Update per-CPU kthreads documentation

From: Paul E. McKenney
Date: Tue Mar 03 2015 - 11:37:58 EST


From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
Documentation/kernel-per-CPU-kthreads.txt | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/Documentation/kernel-per-CPU-kthreads.txt b/Documentation/kernel-per-CPU-kthreads.txt
index 81fe051c4447..f4cbfe0ba108 100644
--- a/Documentation/kernel-per-CPU-kthreads.txt
+++ b/Documentation/kernel-per-CPU-kthreads.txt
@@ -205,7 +205,9 @@ To reduce its OS jitter, do any of the following:
(based on an earlier one from Gilad Ben-Yossef) that
reduces or even eliminates vmstat overhead for some
workloads at https://lkml.org/lkml/2013/9/4/379.
- e. If running on high-end powerpc servers, build with
+ e. Boot with "elevator=noop" to avoid workqueue use by
+ the block layer.
+ f. If running on high-end powerpc servers, build with
CONFIG_PPC_RTAS_DAEMON=n. This prevents the RTAS
daemon from running on each CPU every second or so.
(This will require editing Kconfig files and will defeat
@@ -213,12 +215,12 @@ To reduce its OS jitter, do any of the following:
due to the rtas_event_scan() function.
WARNING: Please check your CPU specifications to
make sure that this is safe on your particular system.
- f. If running on Cell Processor, build your kernel with
+ g. If running on Cell Processor, build your kernel with
CBE_CPUFREQ_SPU_GOVERNOR=n to avoid OS jitter from
spu_gov_work().
WARNING: Please check your CPU specifications to
make sure that this is safe on your particular system.
- g. If running on PowerMAC, build your kernel with
+ h. If running on PowerMAC, build your kernel with
CONFIG_PMAC_RACKMETER=n to disable the CPU-meter,
avoiding OS jitter from rackmeter_do_timer().

@@ -260,8 +262,12 @@ Purpose: Detect software lockups on each CPU.
To reduce its OS jitter, do at least one of the following:
1. Build with CONFIG_LOCKUP_DETECTOR=n, which will prevent these
kthreads from being created in the first place.
-2. Echo a zero to /proc/sys/kernel/watchdog to disable the
+2. Boot with "nosoftlockup=0", which will also prevent these kthreads
+ from being created. Other related watchdog and softlockup boot
+ parameters may be found in Documentation/kernel-parameters.txt
+ and Documentation/watchdog/watchdog-parameters.txt.
+3. Echo a zero to /proc/sys/kernel/watchdog to disable the
watchdog timer.
-3. Echo a large number of /proc/sys/kernel/watchdog_thresh in
+4. Echo a large number of /proc/sys/kernel/watchdog_thresh in
order to reduce the frequency of OS jitter due to the watchdog
timer down to a level that is acceptable for your workload.
--
1.8.1.5

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