Re: [PATCH 1/2] numa: Set default distance map if needed

[Andrew Jones <drjones@redhat.com>]

On Tue, Oct 12, 2021 at 09:31:55PM +1100, Gavin Shan wrote:
> Hi Igor,
> 
> On 10/12/21 8:40 PM, Igor Mammedov wrote:
> > On Wed,  6 Oct 2021 18:22:08 +0800
> > Gavin Shan <gshan@redhat.com> wrote:
> > 
> > > The following option is used to specify the distance map. It's
> > > possible the option isn't provided by user. In this case, the
> > > distance map isn't populated and exposed to platform. On the
> > > other hand, the empty NUMA node, where no memory resides, is
> > > allowed on ARM64 virt platform. For these empty NUMA nodes,
> > > their corresponding device-tree nodes aren't populated, but
> > > their NUMA IDs should be included in the "/distance-map"
> > > device-tree node, so that kernel can probe them properly if
> > > device-tree is used.
> > > 
> > >    -numa,dist,src=<numa_id>,dst=<numa_id>,val=<distance>
> > > 
> > > So when user doesn't specify distance map, we need to generate
> > > the default distance map, where the local and remote distances
> > > are 10 and 20 separately. This adds an extra parameter to the
> > > exiting complete_init_numa_distance() to generate the default
> > > distance map for this case.
> > > 
> > > Signed-off-by: Gavin Shan <gshan@redhat.com>
> > 
> > 
> > how about error-ing out if distance map is required but
> > not provided by user explicitly and asking user to fix
> > command line?
> > 
> > Reasoning behind this that defaults are hard to maintain
> > and will require compat hacks and being raod blocks down
> > the road.
> > Approach I was taking with generic NUMA code, is deprecating
> > defaults and replacing them with sanity checks, which bail
> > out on incorrect configuration and ask user to correct command line.
> > Hence I dislike approach taken in this patch.
> > 
> > If you really wish to provide default, push it out of
> > generic code into ARM specific one
> > (then I won't oppose it that much (I think PPC does
> > some magic like this))
> > Also behavior seems to be ARM specific so generic
> > NUMA code isn't a place for it anyways
> > 
> 
> Thanks for your comments.
> 
> Yep, Lets move the logic into hw/arm/virt in v3 because I think simply
> error-ing out will block the existing configuration where the distance
> map isn't provided by user. After moving the logic to hw/arm/virt,
> this patch is consistent with PATCH[02/02] and the specific platform
> is affected only.

Please don't move anything NUMA DT generic to hw/arm/virt. If the spec
isn't arch-specific, then the modeling shouldn't be either.

If you want to error-out for all configs missing the distance map, then
you'll need compat code. If you only want to error-out for configs that
have empty NUMA nodes and are missing a distance map, then you don't
need compat code, because those configs never worked before anyway.

Thanks,
drew

> 
> 
> > > ---
> > >   hw/core/numa.c | 13 +++++++++++--
> > >   1 file changed, 11 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/hw/core/numa.c b/hw/core/numa.c
> > > index 510d096a88..fdb3a4aeca 100644
> > > --- a/hw/core/numa.c
> > > +++ b/hw/core/numa.c
> > > @@ -594,7 +594,7 @@ static void validate_numa_distance(MachineState *ms)
> > >       }
> > >   }
> > > -static void complete_init_numa_distance(MachineState *ms)
> > > +static void complete_init_numa_distance(MachineState *ms, bool is_default)
> > >   {
> > >       int src, dst;
> > >       NodeInfo *numa_info = ms->numa_state->nodes;
> > > @@ -609,6 +609,8 @@ static void complete_init_numa_distance(MachineState *ms)
> > >               if (numa_info[src].distance[dst] == 0) {
> > >                   if (src == dst) {
> > >                       numa_info[src].distance[dst] = NUMA_DISTANCE_MIN;
> > > +                } else if (is_default) {
> > > +                    numa_info[src].distance[dst] = NUMA_DISTANCE_DEFAULT;
> > >                   } else {
> > >                       numa_info[src].distance[dst] = numa_info[dst].distance[src];
> > >                   }
> > > @@ -716,13 +718,20 @@ void numa_complete_configuration(MachineState *ms)
> > >            * A->B != distance B->A, then that means the distance table is
> > >            * asymmetric. In this case, the distances for both directions
> > >            * of all node pairs are required.
> > > +         *
> > > +         * The default node pair distances, which are 10 and 20 for the
> > > +         * local and remote nodes separatly, are provided if user doesn't
> > > +         * specify any node pair distances.
> > >            */
> > >           if (ms->numa_state->have_numa_distance) {
> > >               /* Validate enough NUMA distance information was provided. */
> > >               validate_numa_distance(ms);
> > >               /* Validation succeeded, now fill in any missing distances. */
> > > -            complete_init_numa_distance(ms);
> > > +            complete_init_numa_distance(ms, false);
> > > +        } else {
> > > +            complete_init_numa_distance(ms, true);
> > > +            ms->numa_state->have_numa_distance = true;
> > >           }
> > >       }
> > >   }
> > 
> 
> Thanks,
> Gavin
>