From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58793) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zbhky-0004Qc-Kl for qemu-devel@nongnu.org; Tue, 15 Sep 2015 00:22:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Zbhkt-0005kk-O1 for qemu-devel@nongnu.org; Tue, 15 Sep 2015 00:22:12 -0400 Received: from e19.ny.us.ibm.com ([129.33.205.209]:47744) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zbhkt-0005kT-KD for qemu-devel@nongnu.org; Tue, 15 Sep 2015 00:22:07 -0400 Received: from /spool/local by e19.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 15 Sep 2015 00:22:06 -0400 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable From: Michael Roth In-Reply-To: <20150915040300.19285.85127@loki> References: <1442194913-26545-1-git-send-email-david@gibson.dropbear.id.au> <1442194913-26545-3-git-send-email-david@gibson.dropbear.id.au> <20150915040300.19285.85127@loki> Message-ID: <20150915042155.19285.34435@loki> Date: Mon, 14 Sep 2015 23:21:55 -0500 Subject: Re: [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: David Gibson , bharata@linux.vnet.ibm.com, aik@ozlabs.ru Cc: pbonzini@redhat.com, qemu-ppc@nongnu.org, agraf@suse.de, qemu-devel@nongnu.org Quoting Michael Roth (2015-09-14 23:03:00) > Quoting David Gibson (2015-09-13 20:41:53) > > 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 construct= ed. > > 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=3D2T, for example, there are 8192 objects under the same pare= nt. > > = > > The QOM interfaces aren't really designed for this. In particular > > object_property_add() with [*] has O(n^2) time complexity (in the numbe= r 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 c= an > > 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 t= ime > > of qemu with maxmem=3D2T from ~20 minutes to ~4 seconds. > > = > > Signed-off-by: David Gibson > > Cc: Bharata B Rao > = > This is the second patch I've seen that drops use of "[*]" for > performance reasons, but looking at the code I don't really see > any reason that logic can't be implemented in object_property_add() > in O(n) time. For instance I think it can be achieved by > storing/hashing the base string to an array of auto-incremented > indicies that we update whenever a child with the corresponding > [n] format is added. > = > I wouldn't hold this real fix up for that though, and in fact the > use of DRC indexes make for much easier debugging anyway so I'd > probably still prefer this approach anyway. Well, along that line, one small nit: I think %x would be a bit easier to correlate with the DRC indexes as we use them elsewhere. Reviewed-by still stands though. > = > Reviewed-by: Michael Roth > = > > --- > > 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 =3D > > SPAPR_DR_CONNECTOR(object_new(TYPE_SPAPR_DR_CONNECTOR)); > > + char *prop_name; > > = > > g_assert(type); > > = > > drc->type =3D type; > > drc->id =3D id; > > - object_property_add_child(owner, "dr-connector[*]", OBJECT(drc), N= ULL); > > + prop_name =3D 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 > >=20