On Wed, Sep 9, 2015 at 11:28 PM, David Gibson <da...@gibson.dropbear.id.au> wrote: > The dynamic reconfiguration (hotplug) code for the pseries machine type > uses a "DR connector" QOM object for each resource it will be possible > to hotplug. Each of these is added to its owner using > object_property_add_child(owner, "dr-connector[*], ...); >
> This works ok for most cases, but gets ugly when allowing large amounts of > hotplugged RAM. For RAM, there's a DR connector object for every 256MB of > potential memory. So if maxmem=2T, for example, there are >250,000 objects > under the same parent. > > The QOM interfaces aren't really designed for this. In particular > object_property_add() has O(n^2) time complexity (in the number of existing > children) for the [*] case. First it has a linear search through array > indices to find a free slot, each of which is attempted to a recursive call > to object_property_add() with a specific [N]. Those calls are O(n) because > there's a linear search through all properties to check for duplicates. > Does this help? I think it's already queued: http://lists.nongnu.org/archive/html/qemu-devel/2015-07/msg05790.html Regards, Peter > For the specific case of DR connectors, we already have a sufficiently > unique index, so we don't need to use the [*] special behaviour. That lets > us reduce the total time for creating the DR objects from O(n^3) to O(n^2). > > O(n^2) is still kind of crappy, but it's enough to reduce the startup time > of qemu with maxmem=2T from ~20 minutes to ~4 seconds. > > Signed-off-by: David Gibson <da...@gibson.dropbear.id.au> > Cc: Bharata B Rao <bhar...@linux.vnet.ibm.com> > --- > hw/ppc/spapr_drc.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c > index c1f664f..4cf3a9b 100644 > --- a/hw/ppc/spapr_drc.c > +++ b/hw/ppc/spapr_drc.c > @@ -463,14 +463,16 @@ sPAPRDRConnector *spapr_dr_connector_new(Object *owner, > { > sPAPRDRConnector *drc = > SPAPR_DR_CONNECTOR(object_new(TYPE_SPAPR_DR_CONNECTOR)); > + char *prop_name = g_strdup_printf("dr-connector[%"PRIu32"]", id); > > g_assert(type); > > drc->type = type; > drc->id = id; > drc->owner = owner; > - object_property_add_child(owner, "dr-connector[*]", OBJECT(drc), NULL); > + object_property_add_child(owner, prop_name, OBJECT(drc), NULL); > object_property_set_bool(OBJECT(drc), true, "realized", NULL); > + g_free(prop_name); > > /* human-readable name for a DRC to encode into the DT > * description. this is mainly only used within a guest in place > -- > 2.4.3 > >
