Messages in this thread | | | Date | Wed, 12 Sep 2018 19:42:36 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4 02/16] sched/core: uclamp: map TASK's clamp values into CPU's clamp groups |
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On Wed, Sep 12, 2018 at 06:35:15PM +0100, Patrick Bellasi wrote: > On 12-Sep 18:12, Peter Zijlstra wrote:
> > No idea; but if you want to go all fancy you can replace he whole > > uclamp_map thing with something like: > > > > struct uclamp_map { > > union { > > struct { > > unsigned long v : 10; > > unsigned long c : BITS_PER_LONG - 10; > > }; > > atomic_long_t s; > > }; > > }; > > That sounds really cool and scary at the same time :) > > The v:10 requires that we never set SCHED_CAPACITY_SCALE>1024 > or that we use it to track a percentage value (i.e. [0..100]).
Or we pick 11 bits, it seems unlikely that capacity be larger than 2k.
> One of the last patches introduces percentage values to userspace. > But, I was considering that in kernel space we should always track > full scale utilization values. > > The c:(BITS_PER_LONG-10) restricts the range of concurrently active > SE refcounting the same clamp value. Which, for some 32bit systems is > only 4 milions among tasks and cgroups... maybe still reasonable...
Yeah, on 32bit having 4M tasks seems 'unlikely'.
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