Re: [PATCH v2] pc: q35: Bump max_cpus to 1024

[Gerd Hoffmann]

On Fri, Nov 18, 2022 at 09:55:35AM +0100, Dario Faggioli wrote:
> Keep the old limit of 288 for machine versions 7.2 and earlier.
> 
> Signed-off-by: Dario Faggioli <dfaggioli@suse.com>
> ---
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Richard Henderson <richard.henderson@linaro.org>
> Cc: Eduardo Habkost <eduardo@habkost.net>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
> ---
> Changes from v1:
> - fix actually keeping the old max value for the 7.2 machine type,
>   which was the original goal, but was done wrongly
> 
> ---
> This is related to:
> 
> c705d0d8d6ed1a520b1ff92cb2f83fef19522d30.camel@suse.com/">https://lore.kernel.org/qemu-devel/c705d0d8d6ed1a520b1ff92cb2f83fef19522d30.camel@suse.com/
> 
> With this applied to QEMU, I've been able to start a VM with as high as
> 980 vCPUs (even if I was on an host with 384 pCPUs, so everything was
> super slow!). After that, I started to see messages like this:
> 
> "SMBIOS 2.1 table length 66822 exceeds 65535"

We finally have smbios 3.0 support in both seabios and edk2, so we can
use that to avoid problems like this.  So when raising the limits for
new machine types we should also flip the smbios default to 3.0.

take care,
  Gerd