On Wed, 6 Mar 2019 18:16:08 +0000
Daniel P. Berrangé <berrange@xxxxxxxxxx> wrote:
> On Wed, Mar 06, 2019 at 06:33:25PM +0100, Igor Mammedov wrote:
> > Amend -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@xxxxxxxxxx>
> > ---
> > numa.c | 5 +++++
> > qemu-options.hx | 12 ++++++++----
> > 2 files changed, 13 insertions(+), 4 deletions(-)
> >
> > diff --git a/numa.c b/numa.c
> > index 3875e1e..42838f9 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 + warn_report("Parameter -numa node,mem is obsolete,"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");
>
> My comments from v1 still apply. We must not do this as long as
> libvirt has no choice but to continue using this feature.
It has a choice to use 'memdev' whenever creating a new VM and continue using 'mem' with exiting VMs.
>
> > }
> > if (node->has_memdev) {
> > Object *o;
> > @@ -407,6 +409,9 @@ void numa_complete_configuration(MachineState *ms)
> > if (i == nb_numa_nodes) {
> > assert(mc->numa_auto_assign_ram);
> > mc->numa_auto_assign_ram(mc, numa_info, nb_numa_nodes, ram_size);
> > + warn_report("Default splitting of RAM between nodes is obsolete,"
> > + " Use '-numa node,memdev' to explicitly define RAM"
> > + " allocation per node");
> > }
> >
> > numa_total = 0;
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index 1cf9aac..61035cb 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -206,10 +206,14 @@ For example:
> > -numa cpu,node-id=0,socket-id=0 -numa cpu,node-id=1,socket-id=1
> > @end example
> >
> > -@samp{mem} assigns a given RAM amount to a node. @samp{memdev}
> > -assigns RAM from a given memory backend device to a node. If
> > -@samp{mem} and @samp{memdev} are omitted in all nodes, RAM is
> > -split equally between them.
> > +@samp{memdev} assigns RAM from a given memory backend device to a node.
> > +
> > +Legacy options/behaviour: @samp{mem} assigns a given RAM amount to a node.
> > +If @samp{mem} and @samp{memdev} are omitted in all nodes, RAM is split equally
> > +between them. Option @samp{mem} and default RAM splitting are obsolete as they
> > +do not provide means to manage RAM on the host side and only allow QEMU to fake
> > +NUMA support which in practice could degrade VM performance.
> > +It's advised to always explicitly configure NUMA RAM by using the @samp{memdev} option.
> >
> > @samp{mem} and @samp{memdev} are mutually exclusive. Furthermore,
> > if one node uses @samp{memdev}, all of them have to use it.
> > --
> > 2.7.4
> >
>
> Regards,
> Daniel
--
libvir-list mailing list
libvir-list@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/libvir-list
