Re: [Qemu-devel] [PATCH v4] NUMA: Enable adding NUMA node implicitly

[Dou Liyang]

Deer Eduardo,

At 10/26/2017 04:02 PM, Eduardo Habkost wrote:
> Hi,
>
> Sorry for taking so long to review it:

Not matter. It's my honor!

> On Mon, Oct 23, 2017 at 09:33:42AM +0800, Dou Liyang wrote:

[...]

> > +     */
> > +    if (ram_slots > 0 && QTAILQ_EMPTY(&numa_opts->head)) {
> > +        if (mc->auto_enable_numa_with_memhp) {
>
> If you move the code after qemu_opts_foreach(), you could just
> check if nb_numa_nodes is 0 instead of peeking at
> numa_opts->head.
>
>
> > +            qemu_opts_parse_noisily(numa_opts, "node", true);
> > +        }
> > +    }
>
> Calling qemu_opts_parse*() has additional user-visible side
> effects (it can make -writeconfig include the new option,
> depending on the initialization ordering).  Affecting QemuOpts
> depending on the machine-type breaks the separation between
> machine configuration from machine initialization, so I would
> like to avoid it.
Yes, Indeed. Thank you so much for kind explanation!

> We could simply call parse_numa_node() (after making it increment
> nb_numa_nodes automatically).

Yes, I will use it in the next version.

> e.g.:
>
>
> diff --git a/numa.c b/numa.c
> index 8d78d959f6..da18e42ce7 100644
> --- a/numa.c
> +++ b/numa.c
> @@ -216,6 +216,7 @@ static void parse_numa_node(MachineState *ms, 
> NumaNodeOptions *node,
>      }
>      numa_info[nodenr].present = true;
>      max_numa_nodeid = MAX(max_numa_nodeid, nodenr + 1);
> +    nb_numa_nodes++;
>  }
>
>  static void parse_numa_distance(NumaDistOptions *dist, Error **errp)
> @@ -282,7 +283,6 @@ static int parse_numa(void *opaque, QemuOpts *opts, Error 
> **errp)
>          if (err) {
>              goto end;
>          }
> -        nb_numa_nodes++;
>          break;
>      case NUMA_OPTIONS_TYPE_DIST:
>          parse_numa_distance(&object->u.dist, &err);
> @@ -433,6 +433,26 @@ void parse_numa_opts(MachineState *ms)
>          exit(1);
>      }
>
> +    /*
> +     * If memory hotplug is enabled (slots > 0) but without '-numa'
> +     * options explicitly on CLI, guestes will break.
> +     *
> +     *   Windows: won't enable memory hotplug without SRAT table at all
> +     *
> +     *   Linux: if QEMU is started with initial memory all below 4Gb
> +     *   and no SRAT table present, guest kernel will use nommu DMA ops,
> +     *   which breaks 32bit hw drivers when memory is hotplugged and
> +     *   guest tries to use it with that drivers.
> +     *
> +     * Enable NUMA implicitly by adding a new NUMA node automatically.
> +     */
> +    if (ms->ram_slots > 0 && nb_numa_nodes == 0 &&
> +        mc->auto_enable_numa_with_memhp) {
> +        NumaNodeOptions node = { };
> +        parse_numa_node(ms, &node, &error_abort);
> +    }
> +
> +
>      assert(max_numa_nodeid <= MAX_NODES);
>
>      /* No support for sparse NUMA node IDs yet: */
>
> > +
> > +    if (qemu_opts_foreach(numa_opts, parse_numa, ms, NULL)) {
> >          exit(1);
> >      }
> >
> > diff --git a/vl.c b/vl.c
> > index 0723835..516d0c9 100644
> > --- a/vl.c
> > +++ b/vl.c
> > @@ -4677,8 +4677,6 @@ int main(int argc, char **argv, char **envp)
> >      default_drive(default_floppy, snapshot, IF_FLOPPY, 0, FD_OPTS);
> >      default_drive(default_sdcard, snapshot, IF_SD, 0, SD_OPTS);
> >
> > -    parse_numa_opts(current_machine);
> > -
> >      if (qemu_opts_foreach(qemu_find_opts("mon"),
> >                            mon_init_func, NULL, NULL)) {
> >          exit(1);
> > @@ -4728,6 +4726,7 @@ int main(int argc, char **argv, char **envp)
> >      current_machine->boot_order = boot_order;
> >      current_machine->cpu_model = cpu_model;
> >
> > +    parse_numa_opts(current_machine, ram_slots);
>
> Why did you add a ram_slots argument if it's already present at
> current_machine->ram_slots?

Oops, Forgot to update it after moving it behind the setup of
current_machine. will remove the redundant ram_slots argument.

Thanks,
        dou
> >      /* parse features once if machine provides default cpu_type */
> >      if (machine_class->default_cpu_type) {
> > --
> > 2.5.5