[PATCH] doc: nohz_full already implies rcu_nocbs

[PATCH] doc: nohz_full already implies rcu_nocbs

[Tudor Brindus]

From Documentation/admin-guide/kernel-parameters.txt, specifically the
last sentence:

 nohz_full=      [KNL,BOOT,SMP,ISOL]
        The argument is a cpu list, as described above.
        In kernels built with CONFIG_NO_HZ_FULL=y, set
        the specified list of CPUs whose tick will be stopped
        whenever possible. The boot CPU will be forced outside
        the range to maintain the timekeeping.  Any CPUs
        in this list will have their RCU callbacks offloaded,
        just as if they had also been called out in the
        rcu_nocbs= boot parameter.

The kernel or-s the nohz_full cpumask into the rcu_nocbs cpumask at
startup, and uses that.

Signed-off-by: Tudor Brindus <me@tbrindus.ca>
---
 doc/guides/howto/pvp_reference_benchmark.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/doc/guides/howto/pvp_reference_benchmark.rst b/doc/guides/howto/pvp_reference_benchmark.rst
index 484de3b7db..1043356b3d 100644
--- a/doc/guides/howto/pvp_reference_benchmark.rst
+++ b/doc/guides/howto/pvp_reference_benchmark.rst
@@ -48,7 +48,7 @@ Host tuning
 
    .. code-block:: console
 
-      intel_pstate=disable mce=ignore_ce default_hugepagesz=1G hugepagesz=1G hugepages=6 isolcpus=2-7 rcu_nocbs=2-7 nohz_full=2-7 iommu=pt intel_iommu=on
+      intel_pstate=disable mce=ignore_ce default_hugepagesz=1G hugepagesz=1G hugepages=6 isolcpus=2-7 nohz_full=2-7 iommu=pt intel_iommu=on
 
 #. Disable hyper-threads at runtime if necessary or if BIOS is not accessible:
 
@@ -278,7 +278,7 @@ Guest tuning
 
    .. code-block:: console
 
-      default_hugepagesz=1G hugepagesz=1G hugepages=1 intel_iommu=on iommu=pt isolcpus=1,2 rcu_nocbs=1,2 nohz_full=1,2
+      default_hugepagesz=1G hugepagesz=1G hugepages=1 intel_iommu=on iommu=pt isolcpus=1,2 nohz_full=1,2
 
 #. Disable NMIs:
 
-- 
2.30.2

Re: [PATCH] doc: nohz_full already implies rcu_nocbs

[Thomas Monjalon]

08/02/2022 04:50, Tudor Brindus:
> From Documentation/admin-guide/kernel-parameters.txt, specifically the
> last sentence:
> 
>  nohz_full=      [KNL,BOOT,SMP,ISOL]
>         The argument is a cpu list, as described above.
>         In kernels built with CONFIG_NO_HZ_FULL=y, set
>         the specified list of CPUs whose tick will be stopped
>         whenever possible. The boot CPU will be forced outside
>         the range to maintain the timekeeping.  Any CPUs
>         in this list will have their RCU callbacks offloaded,
>         just as if they had also been called out in the
>         rcu_nocbs= boot parameter.
> 
> The kernel or-s the nohz_full cpumask into the rcu_nocbs cpumask at
> startup, and uses that.
> 
> Signed-off-by: Tudor Brindus <me@tbrindus.ca>

Applied, thanks.