Wilco Dijkstra <wilco.dijks...@arm.com> writes: > Hi Richard, > >> The problem is that you're effectively asking for these values to be >> taken on faith without providing any analysis and without describing >> how you arrived at the new numbers. Did you try other values too? >> If so, how did they compare with the numbers that you finally chose? >> At least that would give an indication of where the boundaries are. > > Yes, I obviously tried other values, pretty much all in range 1-20. There is > generally a range of 4-5 values that are very similar in size, and then you > choose one in the middle which also looks good for performance. > >> For example, it's easier to believe that 8 is the right value for -Os if >> you say that you tried 9 and 7 as well, and they were worse than 8 by X% >> and Y%. This would also help anyone who wants to tweak the numbers >> again in future. > > For -Os, the size range for values 6-10 is within 0.01% so they are virtually > identical and I picked the median. Whether this will remain best in the future > is unclear since it depends on so many things, so at some point it needs > to be looked at again, just like most other tunings.
Thanks. These details are useful. For example, if someone finds a compelling reason to bump the new values by +/-2 (to help with a particular test case) then it sounds we should accept that, since it wouldn't conflict with your work. So the patch is OK, thanks. (FWIW, I tried building a linux kernel I had lying around at -Os, which also showed an improvement of ~0.07%.) Richard
