Hi Jan, > -----Original Message----- > From: Jan Beulich <jbeul...@suse.com> > Sent: 2022年7月18日 16:10 > To: Wei Chen <wei.c...@arm.com> > Cc: nd <n...@arm.com>; Andrew Cooper <andrew.coop...@citrix.com>; George > Dunlap <george.dun...@citrix.com>; Stefano Stabellini > <sstabell...@kernel.org>; Wei Liu <w...@xen.org>; Roger Pau Monné > <roger....@citrix.com>; xen-devel@lists.xenproject.org; Julien Grall > <jul...@xen.org> > Subject: Re: [PATCH v2 9/9] xen: introduce a Kconfig option to configure > NUMA nodes number > > >>>>> 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. >
Thanks, I will use 64 in next version. Wei Chen > Jan
