On Wednesday 21 Mar 2018 at 15:54:58 (+0000), Patrick Bellasi wrote: > On 21-Mar 14:26, Quentin Perret wrote: > > On Wednesday 21 Mar 2018 at 12:39:21 (+0000), Patrick Bellasi wrote: > > > On 20-Mar 09:43, Dietmar Eggemann wrote: > > > > From: Quentin Perret <[email protected]>
[...] > > So actually, what I can do is add something like > > > > fdom_tot_util += util; > > > > to this loop and compute > > > > energy = cs->power * fdom_tot_util / cs->cap; > > > > only once, instead of having the second loop to compute the energy. We don't > > have to scale the util for each and every CPU since they share the same > > cap state. That would save some divisions and ensure the consistency > > between the selection of the cap state and the associated energy > > computation. What do you think ? > > Right, would say that under the hypothesis the we are in the same > frequency domain (and we are because of fdom->span), that's basically > doing: > > sum_i(P_x * U_i / C_x) => P_x / C_x * sum_i(U_i) > > Where (C_x, P_x) are the EM reported capacity and power for the > expected frequency domain OPP. > Yes that's exactly that. I'll do the change in v2. > > Or maybe you were talking about consistency between several consecutive > > calls to compute_energy() ? > > Nope, the above +1 > [...] > > I agree that it would be nice to document somewhere that > > compute_energy() is unsafe to call without sched_energy_present. > > I can simply add a proper doc comment to this function actually. > > Would that work ? > > Right, it's just that _maybe_ an explicit BUG_ON is improving the > documentation by making more explicit the error on testing ? > > Thus, I would probably add both... but Peter will tell you for sure ;) > Right, but I'm still not sure if the BUG_ON is the right thing to do. I mean, if we really want to make this check, then we could also try to recover into a working state ... If we enter compute_energy() without having an energy model, and if we detect it on time, we could bail out and disable sched_energy_present ASAP with an error message for example. That would let us know if EAS is broken without making the system unusable. Anyways, if there is a general agreement, or if the maintainers think that the BUG_ON is the right thing to do here, I'm happy to change that in future versions :)
