From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47713) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZbIm1-0007iX-5v for qemu-devel@nongnu.org; Sun, 13 Sep 2015 21:41:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZbIm0-0001o5-9v for qemu-devel@nongnu.org; Sun, 13 Sep 2015 21:41:37 -0400 From: David Gibson Date: Mon, 14 Sep 2015 11:41:53 +1000 Message-Id: <1442194913-26545-3-git-send-email-david@gibson.dropbear.id.au> In-Reply-To: <1442194913-26545-1-git-send-email-david@gibson.dropbear.id.au> References: <1442194913-26545-1-git-send-email-david@gibson.dropbear.id.au> Subject: [Qemu-devel] [RFCv2 2/2] spapr: Don't use QOM [*] syntax for DR connectors. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: mdroth@linux.vnet.ibm.com, bharata@linux.vnet.ibm.com, aik@ozlabs.ru Cc: pbonzini@redhat.com, David Gibson , qemu-ppc@nongnu.org, agraf@suse.de, qemu-devel@nongnu.org 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 --- 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 68e0c3e..2f95259 100644 --- a/hw/ppc/spapr_drc.c +++ b/hw/ppc/spapr_drc.c @@ -451,13 +451,16 @@ 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; - 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 -- 2.4.3