On Sun, 2 Oct 2022 15:03:04 +0200 Pim <v...@pronk.nl> wrote: > Hey, > > After noticing this commit: > https://github.com/torvalds/linux/commit/7ab5e10eda02da1d9562ffde562c51055d368e9c > and because of high energy prices here, I did some tests with an energy > monitor to see what the power consumption is for my AMD RX480when its > not used. The RX480 is normally only used to pass through to a vm, but > this vm is mostly switched off so the RX480 is not used.
In order to get the full benefit from the above commit, you'll need to have a system that supports D3cold, otherwise you'll only see an incremental improvement of also placing root ports in D3hot in addition to the device from previous D3host support. I can't really offer any advice regarding systems that support this, I assume it's common in laptops but not so much in desktops. As the patch series describes, we can't simply use PCI config space registers to enter D3cold, we need hardware and firmware support that's generally invoked through ACPI in order to remove power to the slot. Certainly do check to make sure that all the devices under the root port and the root port itself are also in D3hot. If any devices under the bridge remain in a running state, then runtime PM cannot enter D3cold. > The result is that when I boot my system with vfio-pci enabled it uses > ~90Watt (RX480 driver = vfio-pci), but when I boot my system with > vfio-pci disabled (RX480 driver = amdgpu) then my system uses ~80Watt. > Both times the RX480 is in D3hot power state. > > Any idea why using the vfio-pci driver results in ~10Watt more power > consumption? Probably because the native driver can power down more parts of the device than we can via the generic PCI interface that gets us to D3hot. vfio-pci does not have code to reach a device specific low power state. If slot level power control was available, the referenced commit should entirely power-off the device. Thanks, Alex _______________________________________________ vfio-users mailing list vfio-users@redhat.com https://listman.redhat.com/mailman/listinfo/vfio-users
