Re: [libvirt] [PATCH] numa: warn if numa 'mem' option or default RAM splitting between nodes is used.

On Wed, 6 Mar 2019 16:39:38 +0000 Daniel P. Berrangé <berrange(a)redhat.com&gt; wrote: > On Wed, Mar 06, 2019 at 05:30:25PM +0100, Igor Mammedov wrote: > > Ammend -numa option docs and print warnings if 'mem' option or default RAM > > splitting between nodes is used. It's intended to discourage users from using > > configuration that allows only to fake NUMA on guest side while leading > > to reduced performance of the guest due to inability to properly configure > > VM's RAM on the host. > > > > In NUMA case, it's recommended to always explicitly configure guest RAM > > using -numa node,memdev={backend-id} option. > > > > Signed-off-by: Igor Mammedov <imammedo(a)redhat.com&gt; > > --- > > numa.c | 5 +++++ > > qemu-options.hx | 12 ++++++++---- > > 2 files changed, 13 insertions(+), 4 deletions(-) > > > > diff --git a/numa.c b/numa.c > > index 3875e1e..c6c2a6f 100644 > > --- a/numa.c > > +++ b/numa.c > > @@ -121,6 +121,8 @@ static void parse_numa_node(MachineState *ms, NumaNodeOptions *node, > > > > if (node->has_mem) { > > numa_info[nodenr].node_mem = node->mem; > > + warn_report("Parameter -numa node,mem is obsolete," > > + " use -numa node,memdev instead"); > > I don't think we should do this. Libvirt isn't going to stop using this > option in the near term. When users see warnings like this in logs well when it was the only option available libvirt had no other choice, but since memdev became available libvirt should try to use it whenever possible.

> they'll often file bugs reports thinking something is broken which is > not the case here. It's the exact purpose of the warning, to force user asking questions and fix configuration, since he/she obviously not getting NUMA benefits and/or performance-wise

I have to disagree here, I don't like ducking our head and ignoring broken configuration when there is working alternative. As end user I'd hate that problem was hidden from me.