linux-kernel - [tip:sched/core] sched/isolation: Document isolcpus= boot parameter flags, mark it deprecated

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Message-ID: <tip-b0d40d2b22fe48cfcbbfb137fd198be0a1cd8a85@git.kernel.org>
Date:   Tue, 31 Oct 2017 05:05:06 -0700
From:   tip-bot for Frederic Weisbecker <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     cmetcalf@...lanox.com, kernellwp@...il.com, hpa@...or.com,
        torvalds@...ux-foundation.org, riel@...hat.com,
        peterz@...radead.org, paulmck@...ux.vnet.ibm.com,
        tglx@...utronix.de, cl@...ux.com, efault@....de,
        lcapitulino@...hat.com, frederic@...nel.org,
        linux-kernel@...r.kernel.org, mingo@...nel.org
Subject: [tip:sched/core] sched/isolation: Document isolcpus= boot parameter
 flags, mark it deprecated

Commit-ID:  b0d40d2b22fe48cfcbbfb137fd198be0a1cd8a85
Gitweb:     https://git.kernel.org/tip/b0d40d2b22fe48cfcbbfb137fd198be0a1cd8a85
Author:     Frederic Weisbecker <frederic@...nel.org>
AuthorDate: Tue, 31 Oct 2017 04:18:34 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 31 Oct 2017 10:29:39 +0100

sched/isolation: Document isolcpus= boot parameter flags, mark it deprecated

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>
Acked-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Peter Zijlstra <peterz@...radead.org>
Cc: Chris Metcalf <cmetcalf@...lanox.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@...hat.com>
Cc: Mike Galbraith <efault@....de>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Wanpeng Li <kernellwp@...il.com>
Link: http://lkml.kernel.org/r/1509419914-16179-1-git-send-email-frederic@kernel.org
[ Clarified the text some more, marked the boot option deprecated. ]
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 Documentation/admin-guide/kernel-parameters.txt | 39 ++++++++++++++++---------
 1 file changed, 26 insertions(+), 13 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6b99c8b..17eb023 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1727,20 +1727,33 @@
 	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.
+	isolcpus=	[KNL,SMP] Isolate a given set of CPUs from disturbance.
+			[Deprecated - use cpusets instead]
+			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 "cpuset.sched_load_balance" file.
+			  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.
+
 
-			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.
 
 	iucv=		[HW,NET]