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[109.66.7.121]) by smtp.gmail.com with ESMTPSA id n7sm2602185wmd.11.2020.05.06.04.50.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 May 2020 04:50:36 -0700 (PDT) Date: Wed, 6 May 2020 07:50:33 -0400 From: "Michael S. Tsirkin" To: Gerd Hoffmann Subject: Re: [PATCH v2 00/13] microvm: add acpi support Message-ID: <20200506074939-mutt-send-email-mst@kernel.org> References: <20200505134305.22666-1-kraxel@redhat.com> <20200505100010-mutt-send-email-mst@kernel.org> <20200506114635.b5msujuhhbim2kdv@sirius.home.kraxel.org> MIME-Version: 1.0 In-Reply-To: <20200506114635.b5msujuhhbim2kdv@sirius.home.kraxel.org> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.61; envelope-from=mst@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/06 05:50:09 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: Eduardo Habkost , Sergio Lopez , qemu-devel@nongnu.org, Igor Mammedov , Paolo Bonzini , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, May 06, 2020 at 01:46:35PM +0200, Gerd Hoffmann wrote: > On Tue, May 05, 2020 at 10:04:02AM -0400, Michael S. Tsirkin wrote: > > On Tue, May 05, 2020 at 03:42:52PM +0200, Gerd Hoffmann wrote: > > > I know that not supporting ACPI in microvm is intentional. If you st= ill > > > don't want ACPI this is perfectly fine, you can use the usual -no-acp= i > > > switch to toggle ACPI support. > > >=20 > > > These are the advantages you are going to loose then: > > >=20 > > > (1) virtio-mmio device discovery without command line hacks (tweaki= ng > > > the command line is a problem when not using direct kernel boot= ). > > > (2) Better IO-APIC support, we can use IRQ lines 16-23. > > > (3) ACPI power button (aka powerdown request) works. > > > (4) machine poweroff (aka S5 state) works. > >=20 > > Questions > >=20 > > - what's the tradeoff in startup time? >=20 > In the noise. 0.28-0.29 seconds on my hardware to the "i8042: PNP: No > PS/2 controller found" message, no matter whenever acpi is on or off. > With "quiet" (acpi prints more and logging to the serial console is > slow). >=20 > At that point -no-acpi takes one second to figure the ps2 controller > really isn't there (as discussed before). >=20 > Another interesting difference is interrupt handling. >=20 > The -no-acpi version: >=20 > CPU0 =20 > 2: 0 XT-PIC cascade > 4: 284 IO-APIC 4-edge ttyS0 > 8: 0 IO-APIC 8-edge rtc0 > 14: 5399 IO-APIC 14-edge virtio1 > 15: 58 IO-APIC 15-edge virtio0 > NMI: 0 Non-maskable interrupts > [ ... ] >=20 > The acpi version: >=20 > CPU0 =20 > 1: 0 IO-APIC 9-edge ACPI:Ged > 2: 231 IO-APIC 23-fasteoi virtio0 > 3: 6291 IO-APIC 22-fasteoi virtio1 > 4: 1758 IO-APIC 4-edge ttyS0 > 5: 0 IO-APIC 8-edge rtc0 > NMI: 0 Non-maskable interrupts > [ ... ] >=20 > > - what should be the default? >=20 > IMO it makes sense to enable it by default. You get working > power management. You can boot stock cloud images (patched > seabios parses the dsdt to find virtio-mmio devices to boot > from virtio-mmio disks). >=20 > It's easier to leave behind legacy stuff: The kernel trusts the > firmware and doesn't go into "trying harder to find ps2 kbd" mode. > Also what is this "cascade" thing in /proc/interrupts above? [1] >=20 > I expect dropping the rtc is easier with acpi too, the kernel probably > wouldn't try to find it then. Right now seabios needs rtc cmos for > ram size probing, so I didn't test that yet. >=20 > On the other hand I don't really see any disadvantages. The tables are > small ... >=20 > # find /sys/firmware/acpi/tables/ -type f | xargs ls -l > -r--------. 1 root root 70 May 6 06:48 /sys/firmware/acpi/tables/APIC > -r--------. 1 root root 472 May 6 06:48 /sys/firmware/acpi/tables/DSDT > -r--------. 1 root root 268 May 6 06:48 /sys/firmware/acpi/tables/FACP >=20 > ... and simple (no methods) so you can hardly call that "bloat". >=20 > > Based on above I'd be inclined to say default should stay no acpi and > > users should enable acpi with an option. >=20 > I disagree, but I can live with off by default too. We already have > acpi=3DOnOffAuto for X86MachineState, so it is just a matter of handling > microvm.acpi=3Dauto accordingly in x86_machine_is_acpi_enabled(). >=20 > take care, > Gerd >=20 > [1] Rhetorical question, I know what it is. [2] > [2] I don't want remember though. Let's leave flipping the default as a separate patch, to be decided on merits after a bunch of people test with/without. --=20 MST