• Richard Musiol's avatar
    syscall: use CLONE_VFORK and CLONE_VM · 9e6b79a5
    Richard Musiol authored
    This greatly improves the latency of starting a child process when
    the Go process is using a lot of memory. Even though the kernel uses
    copy-on-write, preparation for that can take up to several 100ms under
    certain conditions. All other goroutines are suspended while starting
    a subprocess so this latency directly affects total throughput.
    
    With CLONE_VM the child process shares the same memory with the parent
    process. On its own this would lead to conflicting use of the same
    memory, so CLONE_VFORK is used to suspend the parent process until the
    child releases the memory when switching to to the new program binary
    via the exec syscall. When the parent process continues to run, one
    has to consider the changes to memory that the child process did,
    namely the return address of the syscall function needs to be restored
    from a register.
    
    A simple benchmark has shown a difference in latency of 16ms vs. 0.5ms
    at 10GB memory usage. However, much higher latencies of several 100ms
    have been observed in real world scenarios. For more information see
    comments on #5838.
    
    Fixes #5838
    
    Change-Id: I6377d7bd8dcd00c85ca0c52b6683e70ce2174ba6
    Reviewed-on: https://go-review.googlesource.com/37439Reviewed-by: 's avatarIan Lance Taylor <iant@golang.org>
    Run-TryBot: Ian Lance Taylor <iant@golang.org>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    9e6b79a5
syscall_linux_ppc64x.go 4.5 KB