On Thu, 28 May 2020 11:43:07 -0400 Bryan Steele <bry...@gmail.com>: > On Thu, May 28, 2020 at 04:29:19PM +0200, Solene Rapenne wrote: > > the macro CPU_INFO_FOREACH loop over every CPU but the frequency > > algorithm will raise frequency if one cpu usage goes over a > > threshold but also if the sum of cpu usage goes over another > > threshold. > > > > In the current case, if you have offline cpu (because of hw.smt=0), > > the total will still sum all the idle cpu and it's unlikely that > > the total threshold is ever reached before the per cpu one. > > > > so, this diff skip offline cpus in the loop (robert@ gave me the big > > clue to use cpu_is_online in the loop) > > Thanks for finding this solene! Nice work. > > I've been aware of some issues on AMD with the automatic frequency > scaling and haven't been able to narrow them down. This may not solve > all of them, but does appear to improve things on Ryzen CPUs which > have many cores/threads and no BIOS knob to disable SMT. > > Assuming others agree with the approach.. > > ok brynet@
I think this should help CPU with a lot of cores. If I got the algorithm right this is doing this: if 1 cpu has idle < 25% then scale up OR if sum cpu idle < 33% then scale up when it scales up, it will bump a ticker to 5 and set perf to 100% and check again in the next 100ms. Everytime the loop doesn't need to scale up (but is still at 100% freq) it decrement the ticket. Once the ticket is 0 or less, then the frequency goes to minimum. with the current state, if you have offline cpu, you can never go under 50% of the total idle. So the only way to scale up is to have 1 CPU with less than 25% idle. It's a lot of magic numbers without explanation here. I'm curious if this could be improved. I guess that changing them would tip the balance between responsiveness and battery saving.
