linux-kernel - [PATCH v7] housekeeping: Document isolcpus flags

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Message-Id: <1509419914-16179-1-git-send-email-frederic@kernel.org>
Date:   Tue, 31 Oct 2017 04:18:34 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Christoph Lameter <cl@...ux.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Mike Galbraith <efault@....de>, Rik van Riel <riel@...hat.com>,
        Wanpeng Li <kernellwp@...il.com>
Subject: [PATCH v7] housekeeping: Document isolcpus flags

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@...nel.org>
Cc: Chris Metcalf <cmetcalf@...lanox.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Mike Galbraith <efault@....de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Wanpeng Li <kernellwp@...il.com>
Cc: Luiz Capitulino <lcapitulino@...hat.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