Re: [Qemu-devel] [PATCH v4 6/7] qom: replace object property list with GHashTable

[Andreas Färber]

Am 13.10.2015 um 14:37 schrieb Daniel P. Berrange:
> From: Pavel Fedin <address@hidden>
> 
> ARM GICv3 systems with large number of CPUs create lots of IRQ pins. Since
> every pin is represented as a property, number of these properties becomes
> very large. Every property add first makes sure there's no duplicates.
> Traversing the list becomes very slow, therefore qemu initialization takes
> significant time (several seconds for e. g. 16 CPUs).
> 
> This patch replaces list with GHashTable, making lookup very fast. The only
> drawback is that object_child_foreach() and object_child_foreach_recursive()
> cannot modify their objects during traversal, since GHashTableIter does not
> have modify-safe version. However, the code seems not to modify objects via
> these functions.
> 
> Signed-off-by: Daniel P. Berrange <address@hidden>
> Signed-off-by: Pavel Fedin <address@hidden>

(note these seemed misordered)

I have queued things up to 6/7 on qom-next:
https://github.com/afaerber/qemu-cpu/commits/qom-next

This patch didn't apply and I had to hand-apply one hunk (which I
double-checked, but you never know).

Unfortunately I run into this test failure:

TEST: tests/device-introspect-test... (pid=4094)
  /s390x/device/introspect/list:                                       OK
  /s390x/device/introspect/none:                                       OK
  /s390x/device/introspect/abstract:                                   OK
  /s390x/device/introspect/concrete:
(process:4102): GLib-CRITICAL **: g_hash_table_iter_next: assertion
'ri->version == ri->hash_table->version' failed

(process:4102): GLib-CRITICAL **: g_hash_table_iter_next: assertion
'ri->version == ri->hash_table->version' failed

(process:4102): GLib-CRITICAL **: iter_remove_or_steal: assertion
'ri->version == ri->hash_table->version' failed
**
ERROR:/home/andreas/QEMU/qemu/qom/object.c:867:object_unref: assertion
failed: (obj->ref > 0)
Broken pipe
FAIL
GTester: last random seed: R02S4fa2068506971129a7ebe2323dbe03b7
(pid=4104)
FAIL: tests/device-introspect-test
TEST: tests/qom-test... (pid=4105)
  /s390x/qom/s390-ccw-virtio-2.5:                                      OK
  /s390x/qom/s390-ccw-virtio-2.4:                                      OK
  /s390x/qom/none:                                                     OK
  /s390x/qom/s390-virtio:
WARNING
The s390-virtio machine (non-ccw) is deprecated.
It will be removed in 2.6. Please use s390-ccw-virtio
OK
PASS: tests/qom-test

Are you sure you tested all targets?
Any hunch where this might stem from?

The below patch reveals that the ref count is 0. Might be just a symptom
of the actual problem though.

diff --git a/qom/object.c b/qom/object.c
index 0ac3bc1..9aa6159 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -864,7 +864,7 @@ void object_unref(Object *obj)
     if (!obj) {
         return;
     }
-    g_assert(obj->ref > 0);
+    g_assert_cmpint(obj->ref, >, 0);

     /* parent always holds a reference to its children */
     if (atomic_fetch_dec(&obj->ref) == 1) {

Regards,
Andreas

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