Many thanks, Richard, Andreas, Joachim, and Ben, for your responses! I have a few things to try now. :)
> * what I call the "Cabal test"; namely: > > $ _build/stage1/bin/ghc -O -ilibraries/Cabal/Cabal \ > libraries/Cabal/Cabal/Setup.hs +RTS -s Thanks for spelling it out like that, Ben! I'm slightly embarrassed to say that I hadn't been aware that I could use GHC directly in this way to build a package! Andreas, you wrote: > In general I only compile as linking adds overhead which isn't really part of > GHC. How do I tell GHC to build e.g. nofib/spectral/simple/Main.hs or Cabal without linking? I'll eventually try to distill a wiki page from all this! Cheers, Simon > > * My WIP nofib branch [1] makes nofib much faster and easier to work > with and adds the ability to measure perf counters, in addition to > the usual RTS and cachegrind statistics. > > * My nofib branch produces output in a uniform, easy to consume format > and provides a tool for comparing sets of measurements in this format. > > * My ghc_perf tool [2] is very useful for extracting runtime and perf > statistics from Haskell program runs; furthermore, it produces output > in the same format as expected by the aforementioned nofib-compare > utility. > > * I have a utility [3] which I use to reproducibly build a set of > branches, run the testsuite, nofib, and the Cabal test on each of > them. Admittedly it could use a bit of cleanup but it does its job > reasonably well, making performance measurement a "set it and forget > it" sort of task. > > * We collect and record a complete set of testsuite statistics (saved > to git notes 43]); however, we currently do not import these into > gipeda. > > * We don't currently have a box which can measure reliable timings > (since our builders are nearly all virtualised cloud instances). I'm > going to need to do some shuffling to change this. > > * One potentially useful source of performance information (which sadly > we currently do not exploit) is the -ddump-timing output produced > during head.hackage runs. > > [1] https://gitlab.haskell.org/ghc/nofib/merge_requests/24 > [2] https://gitlab.haskell.org/bgamari/ghc-utils/blob/master/ghc_perf.py > [3] https://gitlab.haskell.org/bgamari/ghc-utils/-/tree/master/build-all > [4] > https://gitlab.haskell.org/ghc/ghc/-/wikis/building/running-tests/performance-tests > > > > A problem in this context is that reliable performance measurements > > require a quiet machine. Closing my browser, and turning off other > > programs is – in my perception – rather inconvenient, particularly > > when I have to do it for a prolonged time. > > > > Ideally I wouldn't have to perform these measurements on my local > > machine at all! Do you usually use a separate machine for this? _Very_ > > convenient would be some kind of bot whom I could tell e.g. > > > > Indeed it is inconvenient. I am in the lucky situation that I have > another machine locally that can be made reasonably quiet without > interfering with my worflow. However, in general > > > @perf-bot compiler perf > > > > …or more concretely > > > > @perf-bot compile nofib/spectral/simple/Main.hs > > > > …or just > > > > @nofib-bot run > > > > … or something like that. > > > > I've noticed that CI now includes a perf-nofib job. But since it > > appears to run on a different machine each time, I'm not sure whether > > it's actually useful for comparing performance. Could it be made more > > useful by running it consistently on the same dedicated machine? > > > Indeed, we currently don't have a dedicated machine for timings. > However, allocations and executable sizes are still useful. > > Nevertheless, as noted above I think that we should make more of an > effort to measure time. I need to do some shuffling of our runners so we > have a quiet bare-metal which can be dedicated to performance > measurement. I'll try to get to this in the next day or so. > > > Another question regarding performing compiler perf measurements > > locally is which build flavour to use: So far I have used the "perf" > > flavour. A problem here is that a full build seems to take close to an > > hour. A rebuild with --freeze1 takes ~15 minutes on my machine. Is > > this the right flavour to use? > > > I think perf is the best option for performance measurement (afterall, > we want to know what users would see). However, it is indeed a bit > painful. > > > BTW what's the purpose of the profiled GHC modules built with this > > flavour which just seem to additionally prolong compile time? I don't > > see a ghc-prof binary or similar in _build/stage1/bin. > > > Indeed; there is little sense in building profiled modules just for > performance measurement. However, I don't believe we currently have a > build flavour which provides comparable optimisation but without the > profiled way. Perhaps we should add one. > > > Also, what's the status of gipeda? The most recent commit at > > https://perf.haskell.org/ghc/ is from "about a year ago"? > > > Indeed the machine which was previously providing gipeda builds is sadly > no longer around; consequently it's on ice at the moment. I would like > to get it going again but recently correctness issues have been taking > up more time than I would like to admit. > > > Sorry for this load of questions and complaints! I do believe though > > that if work on compiler performance was a bit better documented and > > more convenient, we might see even more progress on that front. :) > > > Quite alright! Typing out the points above made me realize that there is > indeed quite a bit of knowledge that the wiki leaves un-said. > > Cheers, > > - Ben > _______________________________________________ ghc-devs mailing list [email protected] http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
