On 08-Jul 14:46, Douglas Raillard wrote: > Hi Patrick, > > On 7/8/19 12:09 PM, Patrick Bellasi wrote: > > On 03-Jul 17:36, Douglas Raillard wrote: > > > On 7/2/19 4:51 PM, Peter Zijlstra wrote: > > > > On Thu, Jun 27, 2019 at 06:15:58PM +0100, Douglas RAILLARD wrote:
[...] > > You are also correct in pointing out that in the steady state > > ramp_boost will not be triggered in that steady state. > > > > IMU, that's for two main reasons: > > a) it's very likely that enqueued <= util_avg > > b) even in case enqueued should turn out to be _slightly_ bigger then > > util_avg, the corresponding (proportional) ramp_boost would be so > > tiny to not have any noticeable effect on OPP selection. > > > > Am I correct on point b) above? > > Assuming you meant "util_avg slightly bigger than enqueued" (which is when > boosting triggers), > then yes since ramp_boost effect is proportional to "task_ue.enqueue - > task_u". It makes it robust > against that. Right :) > > Could you maybe come up with some experimental numbers related to that > > case specifically? > > With: > * an rt-app task ramping up from 5% to 75% util in one big step. The > whole cycle is 0.6s long (0.3s at 5% followed by 0.3s at 75%). This > cycle is repeated 20 times and the average of boosting is taken. > > * a hikey 960 (this impact the frequency at which the test runs at > the beginning of 75% phase, which impacts the number of missed > activations before the util ramped up). > > * assuming an OPP exists for each util value (i.e. 1024 OPPs, so the > effect of boost on consumption is not impacted by OPP capacities > granularity) > > Then the boosting feature would increase the average power > consumption by 3.1%, out of which 0.12% can be considered "spurious > boosting" due to the util taking some time to really converge to its > steady state value. > > In practice, the impact of small boosts will be even lower since > they will less likely trigger the selection of a high OPP due to OPP > capacity granularity > 1 util unit. That's ok for the energy side: you estimate a ~3% worst case more energy on that specific target. By boosting I expect the negative boost to improve. Do you have also numbers/stats related to the negative slack? Can you share a percentage figure for that improvement? Best, Patrick -- #include <best/regards.h> Patrick Bellasi
