Notice how the active OS X builds reaches the limit of 216 jobs and the backlog of OS X jobs increases without decreasing. This is a capacity issue that is likely related to high OS X build costs.
Another thing to notice is that the backlog correlates strongly with time of day in the EST timezone, where the backlog starts to take off after 9am EST.
> "env": "RUST_CHECK_TARGET=dist RUST_CONFIGURE_ARGS=\"--target=aarch64-apple-ios,armv7-apple-ios,armv7s-apple-ios,i386-apple-ios,x86_64-apple-ios --enable-extended --enable-sanitizers --enable-profiler\" SRC=. DEPLOY=1 RUSTC_RETRY_LINKER_ON_SEGFAULT=1 SCCACHE_ERROR_LOG=/tmp/sccache.log MACOSX_DEPLOYMENT_TARGET=10.7\n",
iOS, it seems.
Looking at the other builds,
* s390x Linux
* i686-apple-darwin
* x86_64-apple-darwin
Seems apple is an overall slowpoke.