Re: [PATCH v1 5/6] mm: make vmstat_update periodic run conditional

[Christoph Lameter]

On Tue, 8 May 2012, Gilad Ben-Yossef wrote:

> My line of thought was that if we explicitly choose a scapegoat cpu we
> and the user need to manage this - such as worry about what happens if
> the scapegoats is offlines and let the user explicitly designate the
> scapegoat cpu thus creating another knob, and worrying about what
> happens if the user designate such a cpu but then it goes offlines...

The scapegoat can be chosen on boot. One can f.e. create a file in

/sys/device/syste/cpu called "scapegoat" which contains the number of the
processor chosen. Then one can even write a userspace daemon to automatize
the moving of the processing elsewhere. Could be integrated into something
horrible like irqbalance f.e.

> I figured the user needs to worry about other unbounded work items
> anyway if he cares about where such things are run in the general case,
> but using isolcpus for example.

True. So the scapegoat heuristic could be to pick the first
unisolated cpu.

> The same should be doable with cpusets, except that right now we mark
> unbounded workqueue worker threads as pinned even though they aren't. If
> I understood the discussion, the idea is exactly to stop users from
> putting these threads in non root cpusets. I am not 100% sure why..

Not sure that cpusets is a good thing to bring in here because that is an
optional feature of the kernel and tying basic functionality like this
to cpuset support does not sound right to me.
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