[PATCH v7] housekeeping: Document isolcpus flags

[Frederic Weisbecker]

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 
Cc: Chris Metcalf 
Cc: Rik van Riel 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Mike Galbraith 
Cc: Ingo Molnar 
Cc: Christoph Lameter 
Cc: Paul E. McKenney 
Cc: Wanpeng Li 
Cc: Luiz Capitulino 
---
 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: ,,,
 
-   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.
-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,]
+
+   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.
+  begins at 0 and the maximum value is
+ "number of CPUs in system - 1".
+
+   The format of  is described above.
+
+
 
iucv=   [HW,NET]
 
-- 
2.7.4

[PATCH v7] housekeeping: Document isolcpus flags

[Frederic Weisbecker]

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 
Cc: Chris Metcalf 
Cc: Rik van Riel 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Mike Galbraith 
Cc: Ingo Molnar 
Cc: Christoph Lameter 
Cc: Paul E. McKenney 
Cc: Wanpeng Li 
Cc: Luiz Capitulino 
---
 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: ,,,
 
-   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.
-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,]
+
+   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.
+  begins at 0 and the maximum value is
+ "number of CPUs in system - 1".
+
+   The format of  is described above.
+
+
 
iucv=   [HW,NET]
 
-- 
2.7.4