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documentation: Update per-CPU kthreads documentation

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Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2015-01-25 11:48:18 -08:00
parent c25197841e
commit f1360570f4
1 changed files with 11 additions and 5 deletions
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16
Documentation/kernel-per-CPU-kthreads.txt
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@ -205,7 +205,9 @@ To reduce its OS jitter, do any of the following:
(based on an earlier one from Gilad Ben-Yossef) that (based on an earlier one from Gilad Ben-Yossef) that
reduces or even eliminates vmstat overhead for some reduces or even eliminates vmstat overhead for some
workloads at https://lkml.org/lkml/2013/9/4/379. 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 CONFIG_PPC_RTAS_DAEMON=n. This prevents the RTAS
daemon from running on each CPU every second or so. daemon from running on each CPU every second or so.
(This will require editing Kconfig files and will defeat (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. due to the rtas_event_scan() function.
WARNING: Please check your CPU specifications to WARNING: Please check your CPU specifications to
make sure that this is safe on your particular system. 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 CBE_CPUFREQ_SPU_GOVERNOR=n to avoid OS jitter from
spu_gov_work(). spu_gov_work().
WARNING: Please check your CPU specifications to WARNING: Please check your CPU specifications to
make sure that this is safe on your particular system. 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, CONFIG_PMAC_RACKMETER=n to disable the CPU-meter,
avoiding OS jitter from rackmeter_do_timer(). 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: To reduce its OS jitter, do at least one of the following:
1. Build with CONFIG_LOCKUP_DETECTOR=n, which will prevent these 1. Build with CONFIG_LOCKUP_DETECTOR=n, which will prevent these
kthreads from being created in the first place. 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. 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 order to reduce the frequency of OS jitter due to the watchdog
timer down to a level that is acceptable for your workload. timer down to a level that is acceptable for your workload.