Re: [PATCH 4/4] nohz: Set isolcpus when nohz_full is set

Mike Galbraith
2015-05-18T14:22:21Z

On Mon, 2015-05-18 at 10:07 -0400, Rik van Riel wrote:
> On 05/17/2015 11:29 PM, Mike Galbraith wrote:
> > On Sun, 2015-05-17 at 22:17 -0400, Rik van Riel wrote:
> >> On 05/17/2015 01:30 AM, Mike Galbraith wrote:
> >>
> >>> Given that kernel initiated association to isolcpus, a user turning
> >>> NO_HZ_FULL_ALL on had better not have much generic load to manage. If
> >>> he/she does not have CPUSETS enabled, or should Rik's patch rendering
> >>> isolcpus immutable be merged,
> >>
> >> My patch does not aim to make isolcpus immutable, it aims to make
> >> isolcpus resistent to system management tools (like libvirt)
> >> automatically undoing isolcpus the instant a cpuset with the default
> >> cpus (inherited from the root group) is created.
> >
> > Aim or not, if cpusets is the sole modifier, it'll render isolcpus
> > immutable, no? Cpusets could grow an override to the override I
> > suppose, to regain control of the resource it thinks it manages.
>
> The other way would be to make /sys/devices/system/cpu/isolcpus
> (which Greg KH promised he would queue up for 4.2) writable.

Anything is better than override the override. That's easy, but the
changelog would have to be farmed out to a talented used car salesman.

-Mike