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. > BTW, which CPU did you use to do the experiments? Are the tuning > parameters for that CPU already consistent with the new generic values? This was done on Neoverse N1. Almost no CPUs use per-CPU tuning for this. Cheers, Wilco
