On 18.07.2022 09:51, Wei Chen wrote: >> From: Julien Grall <jul...@xen.org> >> Sent: 2022年7月14日 19:27 >> >> On 14/07/2022 12:10, Jan Beulich wrote: >>> On 14.07.2022 12:14, Wei Chen wrote: >>>>> From: Jan Beulich <jbeul...@suse.com> >>>>> Sent: 2022年7月12日 22:34 >>>>> >>>>> On 08.07.2022 16:54, Wei Chen wrote: >>>>>> --- a/xen/arch/Kconfig >>>>>> +++ b/xen/arch/Kconfig >>>>>> @@ -17,3 +17,14 @@ config NR_CPUS >>>>>> For CPU cores which support Simultaneous Multi-Threading or >>>>> similar >>>>>> technologies, this the number of logical threads which Xen >> will >>>>>> support. >>>>>> + >>>>>> +config NR_NUMA_NODES >>>>>> + int "Maximum number of NUMA nodes supported" >>>>>> + range 1 255 >>>>>> + default "64" >>>>>> + depends on NUMA >>>>> >>>>> Does 1 make sense? That's not going to be NUMA then, I would say. >>>>> >>>> >>>> Ok, we need at least 2 nodes to be a real NUMA. >>>> >>>>> Does the value being (perhaps far) larger than NR_CPUS make sense? >>>>> >>>> >>>> Arm has 128 default NR_CPUS (except some platforms) and x86 has 256. >>>> So I am not very clear about your comments about far larger? As my >>>> Understanding, one node has 2 or 4 cores are very common in a NUMA >>>> System. >>> >>> The defaults are fine. But does it make sense to have 255 nodes when >>> just 32 CPUs were selected? I'm afraid kconfig is going to get in the >>> way, but I think I'd like the upper bound to be min(NR_CPUS, 255). >> >> Looking around NUMA nodes with 0 CPUs exists. So I don't think we should >> tie the two. >> > > Yes, some nodes can only have RAM and some nodes can only have CPUs. > So is it ok to use 2-255 for node range?
Personally I think we shouldn't allow unreasonably high node counts, unless proven by real hardware existing. Which goes hand in hand with me wanting the upper bound to be a power of 2 value, if for nothing else than a hint that using power-of-2 values here is preferable. Hence I'd like to propose 64 or 128 as upper bound, in this order of (my personal) preference. Jan
