At minimum we should make --enable-profiling build with rust-opt. -Jeff
On Wed, Apr 25, 2018 at 11:35 AM, Emilio Cobos Álvarez <emi...@crisal.io> wrote: > There's a fair amount of people bitten by this constantly, which see long > style profiling markers and what's really happening is that they're > profiling a local opt build, and thus the Rust code in style has barely any > optimization and is slow. > > I know that shouldn't be a thing, and that people should --enable-release > for profiling and all that. But given it happens, could we consider > reverting this change? > > -- Emilio > > > On 10/25/17 7:34 PM, Gregory Szorc wrote: >> >> Compiling Rust code with optimizations is significantly slower than >> compiling without optimizations. As was measured in bug 1411081, the >> difference between rustc's -Copt-level 1 and 2 on an i7-6700K (4+4 cores) >> for a recent revision of mozilla-central was 325s/802s wall/CPU versus >> 625s/1282s. This made Rust compilation during Firefox builds stand out as >> a >> long pole and significantly slowed down builds. >> >> Because we couldn't justify the benefits of level 2 for the build time >> overhead it added, we've changed the build system default so Rust is >> compiled with -Copt-level=1 (instead of 2). >> >> Adding --enable-release to your mozconfig (the configuration for builds we >> ship to users) enables -Copt-level=2. (i.e. we didn't change optimization >> settings for builds we ship to users.) >> >> Adding --disable-optimize sets to -Copt-level=0. (This behavior is >> unchanged.) >> >> If you want explicit control over -Copt-level, you can `export >> RUSTC_OPT_LEVEL=<value>` in your mozconfig and that value will always be >> used. --enable-release implies a number of other changes. So if you just >> want to restore the old build system behavior, set this variable in your >> mozconfig. >> >> Also, due to ongoing work around Rust integration in the build system, it >> is dangerous to rely on manual `cargo` invocations to compile Rust because >> bypassing the build system (not using `mach build`) may not use the same >> set of RUSTFLAGS that direct `cargo` invocations do. Things were mostly in >> sync before. But this change and anticipated future changes will cause >> more >> drift. If you want the correct behavior, use `mach`. >> _______________________________________________ >> dev-platform mailing list >> dev-platform@lists.mozilla.org >> https://lists.mozilla.org/listinfo/dev-platform >> > _______________________________________________ > dev-platform mailing list > dev-platform@lists.mozilla.org > https://lists.mozilla.org/listinfo/dev-platform _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
