Hi, On Thu, Sep 3, 2020 at 9:04 AM Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx> wrote: > > Hi, > > On 2020-09-03 21:24, Doug Anderson wrote: > > Hi, > > > > On Thu, Sep 3, 2020 at 8:47 AM Sai Prakash Ranjan > > <saiprakash.ranjan@xxxxxxxxxxxxxx> wrote: > >> > >> On 2020-09-03 19:16, Doug Anderson wrote: > >> > Hi, > >> > > >> > On Thu, Sep 3, 2020 at 2:58 AM Sai Prakash Ranjan > >> > <saiprakash.ranjan@xxxxxxxxxxxxxx> wrote: > >> >> > >> >> Hi, > >> >> > >> >> On 2020-08-18 21:07, Sai Prakash Ranjan wrote: > >> >> > Hi Doug, > >> >> > > >> >> >> > >> >> >> I guess to start, it wasn't obvious (to me) that there were two > >> >> >> choices and we were picking one. Mentioning that the other > >> >> >> alternative was way-based allocation would help a lot. Even if you > >> >> >> can't fully explain the differences between the two, adding something > >> >> >> to the commit message indicating that this is a policy decision (in > >> >> >> other words, both work but each have their tradeoffs) would help. > >> >> >> Something like this, if it's correct: > >> >> >> > >> >> >> In general we try to enable capacity based allocation (instead of the > >> >> >> default way based allocation) since that gives us better performance > >> >> >> with the current software / hardware configuration. > >> >> >> > >> >> > > >> >> > Thanks, I will add it for next version. Let me also go poke some arch > >> >> > teams > >> >> > to understand if we actually do gain something with this selection, who > >> >> > knows > >> >> > we might get some additional details as well. > >> >> > > >> >> > >> >> I got some information from arch team today, to quote them exactly: > >> >> > >> >> 1) What benefits capacity based allocation brings over the default way > >> >> based allocation? > >> >> > >> >> "Capacity based allows finer grain partition. It is not about improved > >> >> performance but more flexibility in configuration." > >> >> > >> >> 2) Retain through power collapse, doesn’t it burn more power? > >> >> > >> >> "This feature is similar to the standard feature of retention. Yes, > >> >> when > >> >> we > >> >> have cache in retention mode it burns more power but it keeps the > >> >> values > >> >> so > >> >> that when we wake up we can get more cache hits." > >> >> > >> >> > >> >> If its good enough, then I will add this info to the commit msg and > >> >> post > >> >> next version. > >> > > >> > Sounds fine to me. I was mostly looking for a high level idea of what > >> > was happening here. I am at least a little curious about the > >> > retention bit. Is that retention during S3, or during some sort of > >> > Runtime PM? Any idea how much power is burned? Unless the power is > >> > miniscule it seems hard to believe that it would be a net win to keep > >> > a cache powered up during S3 unless you're planning on waking up a > >> > lot. > >> > > >> > >> The retention setting is based on sub cache id(SCID), so I think its > >> for > >> runtime pm, the power numbers weren't provided. But I believe these > >> decisions are made after solid testing and not some random > >> approximations. > > > > Right, I believe it was tested, I just wonder if it was tested on a > > phone vs. a laptop. A phone is almost constantly waking up to deal > > with stuff (which is why my phone battery barely lasts till the end of > > the day). Phones also usually have some type of self refresh on their > > panels so they can be suspended even when they look awake which means > > even more constant wakeups. A laptop (especially without panel self > > refresh) may have very different usage models. I'm trying to confirm > > that this setting is appropriate for both classes of devices or if it > > has been only measured / optimized for the cell phone use case. > > > > Could be, but there are windows laptops based on QCOM SoCs where these > must have also been tested (note that this setting can also be in > firmware > and no one would know), but I don't have numbers to quantify. OK, fair enough. Thanks for the discussion. I'm good with a somewhat broad explanation in the commit message then and if we find that this somehow affects power numbers in a bad way we can track down further. -Doug
