wmi added inline comments.
================ Comment at: llvm/include/llvm/IR/PseudoProbe.h:41 // [18:3] - probe id - // [25:19] - reserved + // [25:19] - probe distribution factor // [28:26] - probe type, see PseudoProbeType ---------------- hoy wrote: > hoy wrote: > > wmi wrote: > > > The bits in discriminator is a scare resource. Have you considered using > > > less bits to represent probe distribution factor? I guess it is possible > > > that using a little more coarse grain distribution factor won't affect > > > performance. > > That's a good point. We are using seven bits to represent [0, 100] so that > > integral numbers can be distinguished. Yes, we could use fewer bits to > > represent, say 4 bits to represent only even numbers. We could also not use > > any bits here but instead use the distribution factor of the outer block > > probes when the competition of those bits are high. I can do an experiment > > to see how well that works. > On a second thought, using the distribution factor of block probes for call > probe may not work well since a callsite may be surrounded by more than one > block probes. > > We could use also fewer bits like 6 bits to encode even numbers in the range > [0, 100], or 5 bits to encoding multiples of 3 in [0, 100]. I did a profile > quality measurement with the even number encoding. It's OK overall except for > two SPEC benchmarks. I guess it's a trade-off we'll have to take when there's > a competition on those bits. Could you elaborate a little bit about the case that a callsite is surrounded by more than one block probe? Is it because bb merge like in cfg simplification? Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D93264/new/ https://reviews.llvm.org/D93264 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
