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Mon, 13 Jul 2020 16:13:43 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 696BC11384A6; Mon, 13 Jul 2020 18:13:42 +0200 (CEST) From: Markus Armbruster To: David Gibson Subject: Re: Slow down with: 'Make "info qom-tree" show children sorted' References: <20200527084754.7531-1-armbru@redhat.com> <20200527084754.7531-3-armbru@redhat.com> <49bea110-0a3d-5a40-6647-67b116fb41b5@redhat.com> <5e967e5f-8ae5-01cc-0dfe-f22e0f03b6b3@redhat.com> <87y2nvanya.fsf@dusky.pond.sub.org> <794f6901-5fe3-f7a1-45e7-f277f687cb6b@redhat.com> <87v9iz7cxl.fsf@dusky.pond.sub.org> <20200713111344.23c1b313@umbus.fritz.box> Date: Mon, 13 Jul 2020 18:13:42 +0200 In-Reply-To: <20200713111344.23c1b313@umbus.fritz.box> (David Gibson's message of "Mon, 13 Jul 2020 11:13:44 +1000") Message-ID: <874kqbbdft.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=207.211.31.120; envelope-from=armbru@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/13 02:19:41 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Laurent Vivier , Thomas Huth , berrange@redhat.com, ehabkost@redhat.com, Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , mark.cave-ayland@ilande.co.uk, qemu-devel@nongnu.org, Greg Kurz , =?utf-8?Q?C=C3=A9dr?= =?utf-8?Q?ic?= Le Goater , Paolo Bonzini , Alex =?utf-8?Q?Benn=C3=A9e?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" David Gibson writes: > On Tue, 07 Jul 2020 14:00:06 +0200 > Markus Armbruster wrote: > >> Paolo Bonzini writes: >>=20 >> > On 07/07/20 07:33, Markus Armbruster wrote: =20 >> >> Philippe Mathieu-Daud=C3=A9 writes: >> >> =20 >> >>> On 7/7/20 6:45 AM, Thomas Huth wrote: =20 >> >>>> On 27/05/2020 10.47, Markus Armbruster wrote: =20 >> >>>>> "info qom-tree" prints children in unstable order. This is a pain >> >>>>> when diffing output for different versions to find change. Print = it >> >>>>> sorted. >> >>>>> >> >>>>> Signed-off-by: Markus Armbruster >> >>>>> --- >> >>>>> qom/qom-hmp-cmds.c | 24 ++++++++++++++++-------- >> >>>>> 1 file changed, 16 insertions(+), 8 deletions(-) =20 >> >>>> >> >>>> Hi Markus, >> >>>> >> >>>> this patch causes a slow down of the qtests which becomes quite mas= sive >> >>>> when e.g. using the ppc64 and thourough testing. When I'm running >> >>>> >> >>>> QTEST_QEMU_BINARY=3D"ppc64-softmmu/qemu-system-ppc64" time \ >> >>>> ./tests/qtest/device-introspect-test -m slow | tail -n 10 >> >>>> >> >>>> the test runs for ca. 6m40s here before the patch got applied, and = for >> >>>> mor than 20 minutes after the patch got applied! =20 >> >>=20 >> >> That's surprising. =20 >> > >> > It's a bit surprising indeed, but on the other hand using >> > g_queue_insert_sorted results in a quadratic loop. =20 >>=20 >> The surprising part is that n turns out to be large enough for n^2 to >> matter *that* much. > > Is this another consequence of the ludicrous number of QOM objects we > create for LMB DRCs (one for every 256MiB of guest RAM)? Avoiding that > is on my list. You're talking about machine pseries, I presume. With print_qom_composition() patched to print the number of children, I get $ echo -e 'info qom-tree\nq' | ../qemu/bld/ppc64-softmmu/qemu-system-pp= c64 -S -display none -M pseries -accel qtest -monitor stdio | grep '###' | = sort | uniq -c | sort -k 3n 360 ### 0 children 5 ### 1 children 5 ### 2 children 2 ### 3 children 1 ### 4 children 1 ### 15 children 1 ### 16 children 1 ### 18 children 1 ### 37 children 1 ### 266 children The outlier is /device[5] (spapr-pci-host-bridge) due to its 256 spapr-drc-pci children. I found quite a few machines with similar outliers. ARM machines nuri and smdkc210 together take the cake: they each have a node with 513 children. My stupid n^2 sort is unnoticable in normal, human usage even for n=3D513. > Though avoiding a n^2 behaviour here is probably a good > idea anyway. Agreed.