• Mike Snitzer's avatar
    dm round robin: revert "use percpu 'repeat_count' and 'current_path'" · 37a098e9
    Mike Snitzer authored
    The sloppy nature of lockless access to percpu pointers
    (s->current_path) in rr_select_path(), from multiple threads, is
    causing some paths to used more than others -- which results in less
    IO performance being observed.
    Revert these upstream commits to restore truly symmetric round-robin
    IO submission in DM multipath:
    b0b477c7 dm round robin: use percpu 'repeat_count' and 'current_path'
    802934b2 dm round robin: do not use this_cpu_ptr() without having preemption disabled
    There is no benefit to all this complexity if repeat_count = 1 (which is
    the recommended default).
    Cc: stable@vger.kernel.org # 4.6+
    Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
dm-round-robin.c 5.04 KB