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 still > > > don't want ACPI this is perfectly fine, you can use the usual -no-acpi > > > switch to toggle ACPI support. > > > > > > These are the advantages you are going to loose then: > > > > > > (1) virtio-mmio device discovery without command line hacks (tweaking > > > 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. > > > > Questions > > > > - what's the tradeoff in startup time? > > 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). > > At that point -no-acpi takes one second to figure the ps2 controller > really isn't there (as discussed before). > > Another interesting difference is interrupt handling. > > The -no-acpi version: > > CPU0 > 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 > [ ... ] > > The acpi version: > > CPU0 > 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 > [ ... ] > > > - what should be the default? > > 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). > > 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] > > 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. > > On the other hand I don't really see any disadvantages. The tables are > small ... > > # 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 > > ... and simple (no methods) so you can hardly call that "bloat". > > > Based on above I'd be inclined to say default should stay no acpi and > > users should enable acpi with an option. > > I disagree, but I can live with off by default too. We already have > acpi=OnOffAuto for X86MachineState, so it is just a matter of handling > microvm.acpi=auto accordingly in x86_machine_is_acpi_enabled(). > > take care, > Gerd > > [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. -- MST
