Re: [PATCH 6/6] sched/isolation: Update nohz documentation to explain tick offload

[Thomas Gleixner]

On Thu, 15 Feb 2018, Frederic Weisbecker wrote:

> Update the documentation to reflect the 1Hz tick offload changes.
> 
> Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
> Cc: Chris Metcalf <cmetcalf@xxxxxxxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: Luiz Capitulino <lcapitulino@xxxxxxxxxx>
> Cc: Mike Galbraith <efault@xxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Wanpeng Li <kernellwp@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 1d1d53f..50b9837 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1766,6 +1766,17 @@
>  
>  			nohz
>  			  Disable the tick when a single task runs.
> +
> +			  A residual 1Hz tick is offloaded to workqueues, which you
> +			  need to affine to housekeeping through the global
> +			  workqueue's affinity configured via the
> +			  /sys/devices/virtual/workqueue/cpumask sysfs file, or
> +			  by using the 'domain' flag described below.
> +
> +			  NOTE: by default the global workqueue runs on all CPUs,
> +			  so to protect individual CPUs the 'cpumask' file has to
> +			  be configured manually after bootup.

Hmm. Why don't you set that to the housekeeping cpus by default?

Thanks,

	tglx