On Tue, Jul 26, 2016 at 01:35:50PM +0200, Alexandre DERUMIER wrote:
> Hi Wolfgang,
>
> I just come back from holiday.
Hope you had a good time :-)
>
>
>
> >>Issue #1: The above code currently does not honor our 'hostnodes' option
> >>and breaks when trying to use them together.
>
> mmm indeed. I think this can be improved. I'll try to check that next week.
>
>
>
> >>Issue #2: We create one node per *virtual* socket, which means enabling
> >>hugepages with more virtual sockets than physical numa nodes will die
> >>with the error that the numa node doesn't exist. This should be fixable
> >>as far as I can tell, as nothing really prevents us from putting them on
> >>the same node? At least this used to work and I've already asked this
> >>question at some point. You said the host kernel will try to map them,
> >>yet it worked without issues before, so I'm still not sure about this.
> >>Here's the conversation snippet:
>
> you can create more virtual numa node than physical, only if you don't define
> "hostnodes" option.
>
> (from my point of vue, it's totally useless, as the whole point of numa
> option is to map virtual node to physical node, to avoid memory access
> bottleneck)
Useless, yes, which is why I'm wondering whether this should be
supported/warned about/error...
>
> if hostnodes is defined, you need to have physical numa node available (vm
> with 2 numa node need host with 2 numa node)
>
> With hugepage enabled, I have added a restriction to have hostnode defined,
> because you want to be sure that memory is on same node.
>
>
> # hostnodes
> my $hostnodelists = $numa->{hostnodes};
> if (defined($hostnodelists)) {
> my $hostnodes;
> foreach my $hostnoderange (@$hostnodelists) {
> my ($start, $end) = @$hostnoderange;
> $hostnodes .= ',' if $hostnodes;
> $hostnodes .= $start;
> $hostnodes .= "-$end" if defined($end);
> $end //= $start;
> for (my $i = $start; $i <= $end; ++$i ) {
> die "host NUMA node$i doesn't exist\n" if ! -d
> "/sys/devices/system/node/node$i/";
> }
> }
>
> # policy
> my $policy = $numa->{policy};
> die "you need to define a policy for hostnode $hostnodes\n"
> if !$policy;
> $mem_object .= ",host-nodes=$hostnodes,policy=$policy";
> } else {
> die "numa hostnodes need to be defined to use hugepages" if
> $conf->{hugepages};
> }
>
>
> >>Issue #3: Actually just an extension to #2: we currently cannot enable
> >>NUMA at all (even without hugepages) when there are more virtual sockets
> >>than physical numa nodes, and this used to work. The big question is
> >>now: does this even make sense? Or should we tell users not to do this?
>
> That's strange, it should work if you don't defined hugepages and hostnodes
> option(in numaX)
Actually this one was my own faulty configuration, sorry.
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