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

[Jane Malalane <Jane.Malalane@xxxxxxxxxx>]

On 09/02/2022 10:31, 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 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.
> 
> Suggested-by: Edwin Torok <edvin.torok@xxxxxxxxxx>
> Signed-off-by: Jane Malalane <jane.malalane@xxxxxxxxxx>
> ---
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
> CC: Wei Liu <wl@xxxxxxx>
> ---
>   xen/arch/x86/dom0_build.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/xen/arch/x86/dom0_build.c b/xen/arch/x86/dom0_build.c
> index fe24e11b37..e57cc80ef0 100644
> --- 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);
> +
>       return max_vcpus;
>   }
>   
Here I was debating whether to use a printk or a dprintk, as although 
this would be useful for debugging, it gives general info on dom0 vCPU 
topology, as does for e.g. 'Dom0 has maximimum ... vCPUS'. However, I 
defer to the maintainers, as I'm still getting acquainted with Xen (I 
also understand this patch is of minor importance).

Thanks,

Jane.