Hi Jan, Julien, > -----Original Message----- > From: Jan Beulich <[email protected]> > Sent: 2021年8月26日 17:40 > To: Julien Grall <[email protected]>; Wei Chen <[email protected]> > Cc: Bertrand Marquis <[email protected]>; xen- > [email protected]; [email protected] > Subject: Re: [XEN RFC PATCH 26/40] xen/arm: Add boot and secondary CPU to > NUMA system > > On 26.08.2021 10:49, Julien Grall wrote: > > On 26/08/2021 08:24, Wei Chen wrote: > >>> -----Original Message----- > >>> From: Julien Grall <[email protected]> > >>> Sent: 2021年8月26日 0:58 > >>> On 11/08/2021 11:24, Wei Chen wrote: > >>>> --- a/xen/arch/arm/smpboot.c > >>>> +++ b/xen/arch/arm/smpboot.c > >>>> @@ -358,6 +358,12 @@ void start_secondary(void) > >>>> */ > >>>> smp_wmb(); > >>>> > >>>> + /* > >>>> + * If Xen is running on a NUMA off system, there will > >>>> + * be a node#0 at least. > >>>> + */ > >>>> + numa_add_cpu(cpuid); > >>>> + > >>> > >>> On x86, numa_add_cpu() will be called before the pCPU is brought up. I > >>> am not quite too sure why we are doing it differently here. Can you > >>> clarify it? > >> > >> Of course we can invoke numa_add_cpu before cpu_up as x86. But in my > tests, > >> I found when cpu bring up failed, this cpu still be add to NUMA. > Although > >> this does not affect the execution of the code (because CPU is offline), > >> But I don't think adding a offline CPU to NUMA makes sense. > > > > Right, but again, why do you want to solve the problem on Arm and not > > x86? After all, NUMA is not architecture specific (in fact you move most > > of the code in common). > >
I am not very familiar with x86, so when I was composing this patch series, I always thought that if I could solve it inside Arm Arch, I would solve it inside Arm Arch. That seems a bit conservative, and inappropriate on solving this problem. > > In fact, the risk, is someone may read arch/x86 and doesn't realize the > > CPU is not in the node until late on Arm. > > > > So I think we should call numa_add_cpu() around the same place on all > > the architectures. > > FWIW: +1 I agree. As Jan in this discussion. How about following current x86's numa_add_cpu behaviors in __start_xen, but add some code to revert numa_add_cpu when cpu_up failed (both Arm and x86)? > > Jan
