documentation: Update per-CPU kthreads documentation

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/Documentation/kernel-per-CPU-kthreads.txt b/Documentation/kernel-per-CPU-kthreads.txt
index 81fe051c444715c1fb7be584b29a35ba93736861..f4cbfe0ba1085b4df3067dcc457219699c5c6150 100644 (file)
--- 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.