[PATCH v7] housekeeping: Document isolcpus flags

[Frederic Weisbecker <frederic@kernel.org>]

Document the latest updates on the isolcpus boot option. While at it,
let's also fix the details about the preferred way to isolate a set of
CPUs from the scheduler general domains. Cpusets offer a much better
interface to achieve that.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 40 ++++++++++++++++---------
 1 file changed, 26 insertions(+), 14 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6b99c8b..62bc8b5 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1727,20 +1727,32 @@
 	isapnp=		[ISAPNP]
 			Format: <RDP>,<reset>,<pci_scan>,<verbosity>
 
-	isolcpus=	[KNL,SMP] Isolate CPUs from the general scheduler.
-			The argument is a cpu list, as described above.
-
-			This option can be used to specify one or more CPUs
-			to isolate from the general SMP balancing and scheduling
-			algorithms. You can move a process onto or off an
-			"isolated" CPU via the CPU affinity syscalls or cpuset.
-			<cpu number> begins at 0 and the maximum value is
-			"number of CPUs in system - 1".
-
-			This option is the preferred way to isolate CPUs. The
-			alternative -- manually setting the CPU mask of all
-			tasks in the system -- can cause problems and
-			suboptimal load balancer performance.
+	isolcpus=	[KNL,SMP] Isolate a given set of CPUs from disturbance.
+			Format: [flag-list,]<cpu-list>
+
+			Specify one or more CPUs to isolate from disturbances
+			specified in the flag list (default: domain):
+
+			nohz
+			  Disable the tick when a single task runs.
+			domain
+			  Isolate from the general SMP balancing and scheduling
+			  algorithms. Note that performing domain isolation this way
+			  is irreversible. It's not possible to bring back a CPU to
+			  the domains once isolated through isolcpus. It's strongly
+			  advised to use Cpusets instead to disable scheduler load
+			  balancing through the file "cpuset.sched_load_balance".
+			  It offers a much more flexible interface where CPUs can
+			  move in and out of an isolated set anytime.
+
+			  You can move a process onto or off an "isolated" CPU via
+			  the CPU affinity syscalls or cpuset.
+			  <cpu number> begins at 0 and the maximum value is
+			  "number of CPUs in system - 1".
+
+			The format of <cpu-list> is described above.
+
+
 
 	iucv=		[HW,NET]
 
-- 
2.7.4