Herbert Valerio Riedel writes:

On Wed, May 17, 2017 at 10:56 AM, Simon Peyton Jones via ghc-devs wrote:

...

That's great news! Faster than GHC 7.8! We should advertise this :-).

However, not everything is back to 7.8 levels when looking at the time-dimension, e.g. for regex-tdfa-1.2.2 (with reasonably similar versions of dependencies):

Interesting. I tried comparing build times of regex-tdfa-1.1.8 with GHC 8.0.2 and 8.2.1, yet was unable to reproduce this. Rather 8.2 was significantly faster than 8.0.2 (although not in the profiled build, it seems), 8.0.2: real 2m4.403s user 0m2.233s sys 4m49.319s normal build: <> profiled build: <> 8.2.1-rc2: real 1m37.004s user 0m1.690s sys 4m22.921s normal build: <> profiled build: <> My methodology was roughly, $ cabal unpack regex-tdfa-1.1.8 $ cd regex-tdfa-1.1.8 $ use_component ghc 8.0.2 $ cabal configure ; time cabal build --ghc-options='-fforce-recomp -v +RTS -t -RTS' >| 8.0.2 2>&1 $ use_component ghc 8.2.1-rc2 $ cabal configure ; time cabal build --ghc-options='-fforce-recomp -v +RTS -t -RTS' >| 8.2.1 2>&1 The "normal" and "profiled" build metrics are the +RTS -t lines extract from Cabal's profiled and unprofiled GHC invocations. I believe the RTS timings for 8.0.2 are broken due to a (fixed) RTS bug, although I can't come up with a reference at the moment. Herbert, did these timings come from a VPS? Cheers, - Ben

| We'll need to look at what is going on here as this is a pretty | significant regression. Make a ticket with repro instructions? s | -----Original Message----- | From: Ben Gamari [mailto:ben@smart-cactus.org] | Sent: 20 May 2017 18:20 | To: Herbert Valerio Riedel ; Simon Peyton Jones | | Cc: ghc-devs@haskell.org | Subject: Re: 8.2 and earlier build times | | Ben Gamari writes: | | snip | > | > The "normal" and "profiled" build metrics are the +RTS -t lines | > extract from Cabal's profiled and unprofiled GHC invocations. I | > believe the RTS timings for 8.0.2 are broken due to a (fixed) RTS | bug, | > although I can't come up with a reference at the moment. | > | > | I tried this again with regex-tdfa-1.2.2 and indeed I was able to | reproduce Herbert's result, | | | 8.0.2 | normal: <> | profiled: <> | | 8.2.1-rc2: | normal: <> | profiled: <> | | We'll need to look at what is going on here as this is a pretty | significant regression. | | Cheers, | | - Ben