• Simon Marlow's avatar
    Keep the remembered sets local to each thread during parallel GC · 6a405b1e
    Simon Marlow authored
    This turns out to be quite vital for parallel programs:
      - The way we discover which threads to traverse is by finding
        dirty threads via the remembered sets (aka mutable lists).
      - A dirty thread will be on the remembered set of the capability
        that was running it, and we really want to traverse that thread's
        stack using the GC thread for the capability, because it is in
        that CPU's cache.  If we get this wrong, we get penalised badly by
        the memory system.
    Previously we had per-capability mutable lists but they were
    aggregated before GC and traversed by just one of the GC threads.
    This resulted in very poor performance particularly for parallel
    programs with deep stacks.
    Now we keep per-capability remembered sets throughout GC, which also
    removes a lock (recordMutableGen_sync).
Capability.h 10.7 KB