From 390671e38a7e5701403698673039a8ad8082314d Mon Sep 17 00:00:00 2001 From: David Gibson Date: Tue, 15 Sep 2015 01:18:37 +0200 Subject: [PATCH 01/22] spapr: Don't use QOM [*] syntax for DR connectors. Message-id: <1442279917-3996-1-git-send-email-dgibson@redhat.com> Patchwork-id: 67758 O-Subject: [RHEL7.2 qemu-kvm-rhev PATCH] spapr: Don't use QOM [*] syntax for DR connectors. Bugzilla: 1262143 RH-Acked-by: Laszlo Ersek RH-Acked-by: Laurent Vivier RH-Acked-by: Thomas Huth 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[*], ...); That works ok, mostly, but it means that the property indices are arbitrary, depending on the order in which the connectors are constructed. When we have both memory and cpu hotplug, the connectors will be under the same parent (at least in the current drafts), meaning the indices don't correspond to any meaningful ID. It gets worse when large amounts of hotpluggable RAM is configured. For RAM, there's a DR connector object for every 256MB of potential memory. So if maxmem=2T, for example, there are 8192 objects under the same parent. The QOM interfaces aren't really designed for this. In particular object_property_add() with [*] has O(n^2) time complexity (in the number of existing children): 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. By using a meaningful index value, which we already know is unique we can avoid 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 Cc: Bharata B Rao Tested-by: Bharata B Rao Reviewed-by: Alexey Kardashevskiy Upstream: In spapr-next, not merged upstream Signed-off-by: David Gibson Signed-off-by: Miroslav Rezanina --- hw/ppc/spapr_drc.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c index 5732b49..13ad2a1 100644 --- a/hw/ppc/spapr_drc.c +++ b/hw/ppc/spapr_drc.c @@ -450,14 +450,17 @@ sPAPRDRConnector *spapr_dr_connector_new(Object *owner, { sPAPRDRConnector *drc = SPAPR_DR_CONNECTOR(object_new(TYPE_SPAPR_DR_CONNECTOR)); + char *prop_name; g_assert(type); drc->type = type; drc->id = id; drc->owner = owner; - object_property_add_child(owner, "dr-connector[*]", OBJECT(drc), NULL); + prop_name = g_strdup_printf("dr-connector[%"PRIu32"]", get_index(drc)); + 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 -- 1.8.3.1