Re: [PATCH] x86/dom0: Add log for dom0_nodes and dom0_max_vcpus_max conflict

[Jane Malalane <Jane.Malalane@xxxxxxxxxx>]

On 09/02/2022 11:37, Jan Beulich wrote:
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> On 09.02.2022 11:31, Jane Malalane wrote:
>> This is not a bug. The xen cmdline can request both a NUMA restriction
>> and a vcpu count restriction for Dom0. The node restriction wil always
>> be respected which might mean either using dom0_max_vcpus <
>> opt_dom0_max_vcpus_max
> 
> This is quite normal a case if a range was specified, or did you mean
> opt_dom0_max_vcpus_min? But min and max get applied last anyway, so
> those always override what was derived from dom0_nr_pxms.
Yes, I was just giving context here for what I say in the following 
sentence. Maybe this became more confusing than helpful.
> 
>> or using more vCPUs than pCPUs on a node. In
>> the case where dom0_max_vcpus gets capped at the maximum number of
>> pCPUs for the number of nodes chosen, it can be useful particularly
>> for debugging to print a message in the serial log.
> > The number of vCPU-s Dom0 gets is logged in all cases. And the
> reasons why a certain value is uses depends on more than just
> the number-of-nodes restriction. 
Maybe I should have said 'Dom0 "receiving" %d vCPUS' instead of "using" 
in the serial log, in which case I can amend that to make it clearer 
(that ofc if we still want this change)?
I therefor wonder whether the
> wording as you've chosen it is potentially misleading, and
> properly expressing everything in a single message is going to
> be quite a bit too noisy. Furthermore ...
> 
>> --- a/xen/arch/x86/dom0_build.c
>> +++ b/xen/arch/x86/dom0_build.c
>> @@ -240,6 +240,11 @@ unsigned int __init dom0_max_vcpus(void)
>>       if ( max_vcpus > limit )
>>           max_vcpus = limit;
>>   
>> +    if ( max_vcpus < opt_dom0_max_vcpus_max && max_vcpus > 
>> opt_dom0_max_vcpus_min )
>> +        printk(XENLOG_INFO "Dom0 using %d vCPUs conflicts with request to 
>> use"
>> +               " %d node(s), using up to %d vCPUs\n", 
>> opt_dom0_max_vcpus_max,
>> +               dom0_nr_pxms, max_vcpus);
> 
> ... the function can be called more than once, whereas such a
> message (if we really want it) would better be issued just once.
Yes, that is true and this code would have to live outside of dom0_build.c.
> 
> To answer your later reply to yourself: I think printk() is fine
> here (again assuming we want such a message in the first place);
> it's a boot-time-only message after all.
> 
Okay.

Thank you,

Jane.