Re: [Xen-devel] [PATCH] tools/libxl: make default of max event channels dependant on vcpus

["Jürgen Groß" <jgross@suse.com>]

On 26.03.20 10:45, Juergen Gross wrote:
> Today the maximum number of event channels for a guest is defaulting
> to 1023. For large guests with lots of vcpus this is not enough, as
> e.g. the Linux kernel uses 7 event channels per vcpu, limiting the
> guest to about 140 vcpus.
> 
> Instead of requiring to specify the allowed number of event channels
> via the "event_channels" domain config option, make the default
> depend on the maximum number of vcpus of the guest.
> 
> In order not to regress current configs use 1023 as the minimum
> default setting.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>   tools/libxl/libxl_create.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
> index e7cb2dbc2b..eddd0e98e5 100644
> --- a/tools/libxl/libxl_create.c
> +++ b/tools/libxl/libxl_create.c
> @@ -226,7 +226,7 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
>               b_info->iomem[i].gfn = b_info->iomem[i].start;
>   
>       if (!b_info->event_channels)
> -        b_info->event_channels = 1023;
> +        b_info->event_channels = min(1023, b_info->max_vcpus * 8 + 255);

Sorry, forgot to do "stg refresh", this should be max(), of course.


Juergen