On Thu, Aug 27, 2020 at 9:46 AM Derrick, Jonathan <jonathan.derrick@xxxxxxxxx> wrote: > > On Thu, 2020-08-27 at 17:23 +0100, hch@xxxxxxxxxxxxx wrote: > > On Thu, Aug 27, 2020 at 04:13:44PM +0000, Derrick, Jonathan wrote: > > > On Thu, 2020-08-27 at 06:34 +0000, hch@xxxxxxxxxxxxx wrote: > > > > On Wed, Aug 26, 2020 at 09:43:27PM +0000, Derrick, Jonathan wrote: > > > > > Feel free to review my set to disable the MSI remapping which will > > > > > make > > > > > it perform as well as direct-attached: > > > > > > > > > > https://patchwork.kernel.org/project/linux-pci/list/?series=325681 > > > > > > > > So that then we have to deal with your schemes to make individual > > > > device direct assignment work in a convoluted way? > > > > > > That's not the intent of that patchset -at all-. It was to address the > > > performance bottlenecks with VMD that you constantly complain about. > > > > I know. But once we fix that bottleneck we fix the next issue, > > then to tackle the next. While at the same time VMD brings zero > > actual benefits. > > > > Just a few benefits and there are other users with unique use cases: > 1. Passthrough of the endpoint to OSes which don't natively support > hotplug can enable hotplug for that OS using the guest VMD driver > 2. Some hypervisors have a limit on the number of devices that can be > passed through. VMD endpoint is a single device that expands to many. > 3. Expansion of possible bus numbers beyond 256 by using other > segments. > 4. Custom RAID LED patterns driven by ledctl > > I'm not trying to market this. Just pointing out that this isn't > "bringing zero actual benefits" to many users. > The initial intent of the VMD driver was to allow Linux to find and initialize devices behind a VMD configuration where VMD was required for a non-Linux OS. For Linux, if full native PCI-E is an available configuration option I think it makes sense to recommend Linux users to flip that knob rather than continue to wrestle with the caveats of the VMD driver. Where that knob isn't possible / available VMD can be a fallback, but full native PCI-E is what Linux wants in the end.
