|58||58|| * '''Simon Marlow''' Has been busy implementing and benchmarking a new garbage collector. GHC's current garbage collector is of the parallel "stop-the-world" variety, where to collect the heap all cores stop running the program and collect the heap in parallel. The new collector is a "local heap" collector, in which each core has a private heap that can be collected independently of the other cores, meanwhile there is a shared global heap that is collected (much less frequently) by the usual parallel stop-the-world algorithm. We have a paper describing the new design which has been accepted at ISMM'11 (and will be online shortly). The results are mixed; while on average performance improves with the new collector for parallel programs, the improvements are not dramatic (at least up to 24 cores). The new collector is significantly more complex than GHC's current collector. Hence we do not plan to merge it into the mainline yet, but will maintain it on a git branch for the time being, while we continue to experiment with and tune it. Some improvements from the branch that were independent of the new GC algorithm have already been merged into the mainline, so 7.2.1 will see some small improvements in GC performance and stats reporting.