Messages in this thread | | | Date | Fri, 9 Feb 2018 08:06:49 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 6/6] sched/isolation: Tick offload documentation |
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* Frederic Weisbecker <frederic@kernel.org> wrote:
> Update the documentation to reflect the 1Hz tick offload changes. > > Signed-off-by: Frederic Weisbecker <frederic@kernel.org> > Cc: Chris Metcalf <cmetcalf@mellanox.com> > Cc: Christoph Lameter <cl@linux.com> > Cc: Luiz Capitulino <lcapitulino@redhat.com> > Cc: Mike Galbraith <efault@gmx.de> > Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Rik van Riel <riel@redhat.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Wanpeng Li <kernellwp@gmail.com> > Cc: Ingo Molnar <mingo@kernel.org> > --- > Documentation/admin-guide/kernel-parameters.txt | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 39ac9d4..c851e41 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -1762,7 +1762,11 @@ > specified in the flag list (default: domain): > > nohz > - Disable the tick when a single task runs. > + Disable the tick when a single task runs. A residual 1Hz > + tick is offloaded to workqueues that you need to affine > + to housekeeping through the sysfs file > + /sys/devices/virtual/workqueue/cpumask or using the below > + domain flag.
This is pretty ambiguous and somewhat confusing, I'd suggest something like:
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.
Assuming what I wrote is correct - the CPU isolation config space is pretty confusing all around and should be made a lot more human friendly ...
Thanks,
Ingo
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