Hello, Tejun. 在 2026/9/29 08:42, Tejun Heo 写道: > Hello, Tao. > > On Thu, 24 Sep 2026 13:45:45 +0800, Tao Cui wrote: > >> loading attaches the model to >> that device and switches it away from the builtin linear model, >> detaching the struct_ops restores the builtin model, and the >> struct_ops core owns the program lifetime. > > I don't think attaching should enable the controller. v7 currently turns > it on without the queue freeze and quiesce that ioc_qos_write() goes > through. Attaching can create the ioc if needed like an io.cost.model > write does and switch the model under the same freeze and quiesce, > leaving enabling to io.cost.qos. > > This is different from what I said on v1, where switching back to the > builtin model detached the struct_ops, but with the controller state left > to io.cost.qos it seems more consistent to keep the attachment independent > too. Writing enable=0 or model=linear wouldn't detach the struct_ops, > model=bpf would switch back to the attached model, and only detaching > would remove it. This is the same as the linear coefficients, which are > kept while the BPF model is in use and take effect again when switched > back. >
Done. The implicit enable and the wbt_disable_default() are gone. Attaching now checks disk_live() and creates the ioc under rq_qos_mutex, like blkg_conf_open_bdev() does, and switches the active model under the same freeze and quiesce sequence as the io.cost.model writes. To make sure I understood correctly: attaching switches the active model to the attached BPF model, while model=linear and model=bpf only switch between the attached model and the builtin model without affecting the attachment itself. The attachment survives enable=0, and only .unreg removes it. Please shout if I still got that wrong. >> iocg_init()/iocg_free() >> callbacks, invoked from the iocg policy init and free paths with >> the same per (cgroup, device) lifetime, let models manage their own >> per-cgroup state. > > Existing cgroups don't get iocg_init() on attach and iocg_free() isn't > delivered on detach, so init and free don't pair up. Can you call > iocg_init() for all existing iocgs on attach and iocg_free() for the > remaining ones on detach? That's what sched_ext does with > ops.cgroup_init() and ops.cgroup_exit() on enable and disable. > Done. One note on the implementation: the existing iocgs are walked over q->blkg_list under q->blkcg_mutex, the same walk the blkcg policy teardown uses, rather than over the cgroup tree - this is a per-device walk and the queue is frozen and quiesced at that point. Cgroups without a blkg on the device yet are not missed: their blkg is created later and ioc_pd_init()/ioc_pd_free() deliver the callbacks then, so init and free pair up either way. >> Writing "ctrl=bpf" or "model=bpf" is accepted as a no-op so a saved >> configuration still parses; re-attaching the model requires loading >> the struct_ops again, not writing to this file. > > ctrl keeps describing the coefficients and never reads back "bpf", so > ctrl=bpf shouldn't be accepted. model=bpf should fail when no model is > attached. > Done as suggested; the bpf-ci review of v7 reported the same two. Thanks. Tao> Thanks. > > -- > tejun
