1 files changed, 48 insertions, 1 deletions

diff --git a/Documentation/kernel-per-CPU-kthreads.txt b/Documentation/kernel-per-CPU-kthreads.txt
index cbf7ae412da4..32351bfabf20 100644
--- a/Documentation/kernel-per-CPU-kthreads.txt
+++ b/Documentation/kernel-per-CPU-kthreads.txt
@@ -157,6 +157,53 @@ RCU_SOFTIRQ:  Do at least one of the following:
                 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.      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.      It is not possible to entirely get rid of OS jitter
+                from vmstat_update() on CONFIG_SMP=y systems, 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().
+        e.      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
+                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
+                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 +232,7 @@ Purpose: Offload RCU callbacks from the corresponding CPU.
 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.