On Sat, May 11, 2024, cheng.lin130@xxxxxxxxxx wrote: > > > > > > From: seanjc <seanjc@xxxxxxxxxx> > > > > > > > From: Cheng Lin <cheng.lin130@xxxxxxxxxx> > > > > > > > > > > > > > > Introduce vm's max_halt_poll_ns and override_halt_poll_ns to > > > > > > > debugfs. Provide a way to check and modify them. > > > > > > Why? > > > > > If a vm's max_halt_poll_ns has been set using KVM_CAP_HALT_POLL, > > > > > the module parameter kvm.halt_poll.ns will no longer indicate the maximum > > > > > halt pooling interval for that vm. After introducing these two attributes into > > > > > debugfs, it can be used to check whether the individual configuration of the > > > > > vm is enabled and the working value. > > > > But why is max_halt_poll_ns special enough to warrant debugfs entries? There is > > > > a _lot_ of state in KVM that is configurable per-VM, it simply isn't feasible to > > > > dump everything into debugfs. > > > If we want to provide a directly modification interface under /sys for per-vm > > > max_halt_poll_ns, like module parameter /sys/module/kvm/parameters/halt_poll_ns, > > > using debugfs may be worth. > > Yes, but _why_? I know _what_ a debugs knob allows, but you have yet to explain > > why this > I think that if such an interface is provided, it can be used to check the source of > vm's max_halt_poll_ns, general module parameter or per-vm configuration. > When configured through per-vm, such an interface can be used to monitor this > configuration. If there is an error in the setting through KVMCAP_HALL_POLL, such > an interface can be used to fix or reset it dynamicly. But again, that argument can be made for myriad settings in KVM. And unlike many settings, a "bad" max_halt_poll_ns can be fixed simply by redoing KVM_CAP_HALL_POLL. It's not KVM's responsibility to police userspace for bugs/errors, and IMO a backdoor into max_halt_poll_ns isn't justified.
