Re: [Qemu-devel] [PATCH v5 01/10] vl: Don't allow CPU toplogies with partially filled cores

[David Gibson]

On Fri, Nov 20, 2015 at 06:24:30PM +0530, Bharata B Rao wrote:
> Prevent guests from booting with CPU topologies that have partially
> filled CPU cores or can result in partially filled CPU cores after
> CPU hotplug like
> 
> -smp 15,sockets=1,cores=4,threads=4,maxcpus=16 or
> -smp 15,sockets=1,cores=4,threads=4,maxcpus=17.
> 
> Signed-off-by: Bharata B Rao <address@hidden>

Reviewed-by: David Gibson <address@hidden>

I may have missed a bit of the discussion leading up to this.  What
was the rationale for still allowing partially filled sockets (and
otherwise doing things at core rather than socket level?)

> ---
>  vl.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/vl.c b/vl.c
> index 7d993a5..23a1a1e 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -1248,6 +1248,15 @@ static void smp_parse(QemuOpts *opts)
>              exit(1);
>          }
>  
> +        if (cpus % threads || max_cpus % threads) {
> +            error_report("cpu topology: "
> +                         "sockets (%u) cores (%u) threads (%u) with "
> +                         "smp_cpus (%u) maxcpus (%u) "
> +                         "will result in partially filled cores",
> +                         sockets, cores, threads, cpus, max_cpus);
> +            exit(1);
> +        }
> +
>          smp_cpus = cpus;
>          smp_cores = cores > 0 ? cores : 1;
>          smp_threads = threads > 0 ? threads : 1;

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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