documentation: Update per-CPU kthreads documentation

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

Documentation/kernel-per-CPU-kthreads.txt

@@ -205,20 +205,22 @@ 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
 		this platform's RAS functionality.)  This avoids jitter
 		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.