From: Alexey Kardashevskiy <aik@ozlabs.ru>
To: David Gibson <david@gibson.dropbear.id.au>,
mdroth@linux.vnet.ibm.com, bharata@linux.vnet.ibm.com
Cc: pbonzini@redhat.com, qemu-ppc@nongnu.org, agraf@suse.de,
qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [RFCv2 2/2] spapr: Don't use QOM [*] syntax for DR connectors.
Date: Mon, 14 Sep 2015 18:13:18 +1000 [thread overview]
Message-ID: <55F6819E.7080902@ozlabs.ru> (raw)
In-Reply-To: <1442194913-26545-3-git-send-email-david@gibson.dropbear.id.au>
On 09/14/2015 11:41 AM, David Gibson 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[*], ...);
>
> 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.
20 minutes sounds really cool :)
>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> Cc: Bharata B Rao <bharata@linux.vnet.ibm.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
> 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
>
--
Alexey
next prev parent reply other threads:[~2015-09-14 8:13 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-14 1:41 [Qemu-devel] [RFCv2 0/2] spapr: Cleanups to dynamic reconfiguration mechanism David Gibson
2015-09-14 1:41 ` [Qemu-devel] [RFCv2 1/2] spapr: Remove unnecessary owner field from sPAPRDRConnector David Gibson
2015-09-14 6:23 ` Bharata B Rao
2015-09-14 8:22 ` Alexey Kardashevskiy
2015-09-14 11:45 ` David Gibson
2015-09-14 12:11 ` Paolo Bonzini
2015-09-14 14:06 ` Alexey Kardashevskiy
2015-09-14 14:24 ` Paolo Bonzini
2015-09-16 3:16 ` David Gibson
2015-09-17 15:50 ` Michael Roth
2015-09-17 15:53 ` Paolo Bonzini
2015-09-17 23:03 ` Michael Roth
2015-09-17 15:01 ` Michael Roth
2015-09-15 0:31 ` David Gibson
2015-09-15 0:30 ` David Gibson
2015-09-15 11:05 ` Paolo Bonzini
2015-09-14 1:41 ` [Qemu-devel] [RFCv2 2/2] spapr: Don't use QOM [*] syntax for DR connectors David Gibson
2015-09-14 4:07 ` Bharata B Rao
2015-09-14 4:14 ` David Gibson
2015-09-14 4:41 ` Bharata B Rao
2015-09-14 5:20 ` David Gibson
2015-09-14 8:13 ` Alexey Kardashevskiy [this message]
2015-09-15 4:03 ` Michael Roth
2015-09-15 4:21 ` Michael Roth
2015-09-16 3:18 ` David Gibson
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