Re: [RFC PATCH v2 00/17] Core scheduling v2

[Thomas Gleixner]

On Thu, 25 Apr 2019, Ingo Molnar wrote:
> * Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote:
> > I don't have the data in a format that can be present everything in a clear
> > format but here is an attempt anyway. This is long but the central point
> > that when when a machine is lightly loaded, HT Off generally performs
> > better than HT On and even when heavily utilised, it's still not a
> > guaranteed loss. I only suggest reading after this if you have coffee
> > and time. Ideally all this would be updated with a comparison to core
> > scheduling but I may not get it queued on my test grid before I leave
> > for LSF/MM and besides, the authors pushing this feature should be able
> > to provide supporting data justifying the complexity of the series.
> 
> BTW., a side note: I'd suggest introducing a runtime toggle 'nosmt' 
> facility, i.e. turn a system between SMT and non-SMT execution runtime, 
> with full reversability between these states and no restrictions.

It exists already: /sys/devices/system/cpu/smt/control

Setting it to off will offline all siblings, on will online them again.

Thanks,

	tglx