> > > > > 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. > General speaking, functionality of any kind should not be routed through debugfs, > it really is meant for debug. E.g. it's typically root-only, is not guaranteed > to exist, its population is best-effort, etc. > > Further, if the override_halt_poll_ns under debugfs is set to be writable, it can even > > achieve the setting of per-vm max_halt_poll_ns, as the KVM_CAP_HALL_POLL interface > > does. > > > I do think it would be reasonable to capture the max allowed polling time in > > > the existing tracepoint though, e.g. > > Yes, I agree it. > > It is sufficient to get per-vm max_halt_poll_ns through tracepoint if KVP_CAP_HALL_POLL > > is used as the unique setting interface. > > > > Do you consider it is worth to provide a setting interface other than KVP_CAP_HALL_POLL?
