--- zzzz-none-000/linux-3.10.107/Documentation/kernel-per-CPU-kthreads.txt	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/Documentation/kernel-per-CPU-kthreads.txt	2021-02-04 17:41:59.000000000 +0000
@@ -157,6 +157,73 @@
 		calls and by forcing both kernel threads and interrupts
 		to execute elsewhere.
 
+Name: kworker/%u:%d%s (cpu, id, priority)
+Purpose: Execute workqueue requests
+To reduce its OS jitter, do any of the following:
+1.	Run your workload at a real-time priority, which will allow
+	preempting the kworker daemons.
+2.	A given workqueue can be made visible in the sysfs filesystem
+	by passing the WQ_SYSFS to that workqueue's alloc_workqueue().
+	Such a workqueue can be confined to a given subset of the
+	CPUs using the /sys/devices/virtual/workqueue/*/cpumask sysfs
+	files.	The set of WQ_SYSFS workqueues can be displayed using
+	"ls sys/devices/virtual/workqueue".  That said, the workqueues
+	maintainer would like to caution people against indiscriminately
+	sprinkling WQ_SYSFS across all the workqueues.	The reason for
+	caution is that it is easy to add WQ_SYSFS, but because sysfs is
+	part of the formal user/kernel API, it can be nearly impossible
+	to remove it, even if its addition was a mistake.
+3.	Do any of the following needed to avoid jitter that your
+	application cannot tolerate:
+	a.	Build your kernel with CONFIG_SLUB=y rather than
+		CONFIG_SLAB=y, thus avoiding the slab allocator's periodic
+		use of each CPU's workqueues to run its cache_reap()
+		function.
+	b.	Avoid using oprofile, thus avoiding OS jitter from
+		wq_sync_buffer().
+	c.	Limit your CPU frequency so that a CPU-frequency
+		governor is not required, possibly enlisting the aid of
+		special heatsinks or other cooling technologies.  If done
+		correctly, and if you CPU architecture permits, you should
+		be able to build your kernel with CONFIG_CPU_FREQ=n to
+		avoid the CPU-frequency governor periodically running
+		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.	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
+		reduces or even eliminates vmstat overhead for some
+		workloads at https://lkml.org/lkml/2013/9/4/379.
+	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.
+	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.
+	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().
+
 Name: rcuc/%u
 Purpose: Execute RCU callbacks in CONFIG_RCU_BOOST=y kernels.
 To reduce its OS jitter, do at least one of the following:
@@ -185,7 +252,7 @@
 To reduce its OS jitter, do at least one of the following:
 1.	Use affinity, cgroups, or other mechanism to force these kthreads
 	to execute on some other CPU.
-2.	Build with CONFIG_RCU_NOCB_CPUS=n, which will prevent these
+2.	Build with CONFIG_RCU_NOCB_CPU=n, which will prevent these
 	kthreads from being created in the first place.  However, please
 	note that this will not eliminate OS jitter, but will instead
 	shift it to RCU_SOFTIRQ.
@@ -195,8 +262,12 @@
 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.