Re: [PATCH] sched/fair: Prefer idle CPU to cache affinity

[Peter Zijlstra]

On Tue, Mar 02, 2021 at 01:09:46PM +0530, Srikar Dronamraju wrote:
> > Oh, could be, I didn't grep :/ We could have core code keep track of the
> > smt count I suppose.
> 
> Could we use cpumask_weight(cpu_smt_mask(this_cpu)) instead?

cpumask_weight() is potentially super expensive. With CPUMASK_OFFSTACK
you get at least one more cache miss and then the bitmap might be really
long.

Best to compute the results once and use it later.