On Mon, May 21, 2018 at 11:50:55AM +0100, Patrick Bellasi wrote: > On 18-May 11:55, Joel Fernandes (Google.) wrote: > > From: "Joel Fernandes (Google)" <j...@joelfernandes.org> > > > > Currently there is a chance of a schedutil cpufreq update request to be > > dropped if there is a pending update request. This pending request can > > be delayed if there is a scheduling delay of the irq_work and the wake > > up of the schedutil governor kthread. > > > > A very bad scenario is when a schedutil request was already just made, > > such as to reduce the CPU frequency, then a newer request to increase > > CPU frequency (even sched deadline urgent frequency increase requests) > > can be dropped, even though the rate limits suggest that its Ok to > > process a request. This is because of the way the work_in_progress flag > > is used. > > > > This patch improves the situation by allowing new requests to happen > > even though the old one is still being processed. Note that in this > > approach, if an irq_work was already issued, we just update next_freq > > and don't bother to queue another request so there's no extra work being > > done to make this happen. > > Maybe I'm missing something but... is not this patch just a partial > mitigation of the issue you descrive above? > > If a DL freq increase is queued, with this patch we store the request > but we don't actually increase the frequency until the next schedutil > update, which can be one tick away... isn't it? > > If that's the case, maybe something like the following can complete > the cure?
We already discussed this and thought of this case, I think you missed a previous thread [1]. The outer loop in the kthread_work subsystem will take care of calling sugov_work again incase another request was queued which we happen to miss. So I don't think more complexity is needed to handle the case you're bringing up. thanks! - Joel [1] https://lkml.org/lkml/2018/5/17/668
