Messages in this thread | | | Date | Tue, 6 Sep 2022 07:48:30 -0700 | From | Yury Norov <> | Subject | Re: [PATCH v2 0/5] cpumask: cleanup nr_cpu_ids vs nr_cpumask_bits mess |
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On Tue, Sep 06, 2022 at 01:06:47PM +0100, Valentin Schneider wrote: > On 06/09/22 10:55, Peter Zijlstra wrote: > > On Mon, Sep 05, 2022 at 04:08:15PM -0700, Yury Norov wrote: > >> cpumask subsystem uses nr_cpu_ids and nr_cpumask_bits interchangeably > >> despite that the variables have different meaning and purpose. It makes > >> some cpumask functions broken. > >> > >> This series cleans that mess and adds new config FORCE_NR_CPUS that > >> allows to optimize cpumask subsystem if the number of CPUs is known > >> at compile-time. > > > > Who will use this? Distro's can't, which means 99% of people will not > > use this ever. Is it worth it? > > I'd tend to agree here. > > One extra thing worth noting is CONFIG_CPUMASK_OFFSTACK=n cpumask_size() > still uses NR_CPUS under the hood, despite being (mostly) used to > dynamically allocate cpumasks. So having an unconditionnal > > #define nr_cpumask_bits nr_cpu_ids > > would save up some memory for those allocations.
Thanks, I didn't mention this. This is exactly what I meant by 'cleaning the mess'.
> A quick compile test on x86 defconfig (OFFSTACK=n) gives me: > > Total: Before=18711411, After=18705653, chg -0.03%
All cpumask_size() allocations are runtime, right?
> If it's in the range of barely-half-a-page on other archs, could we just > do that then?
How many is that in terms of I-cache lines?
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