• Tejun Heo's avatar
    block: fix diskstats access · c9959059
    Tejun Heo authored
    There are two variants of stat functions - ones prefixed with double
    underbars which don't care about preemption and ones without which
    disable preemption before manipulating per-cpu counters.  It's unclear
    whether the underbarred ones assume that preemtion is disabled on
    entry as some callers don't do that.
    This patch unifies diskstats access by implementing disk_stat_lock()
    and disk_stat_unlock() which take care of both RCU (for partition
    access) and preemption (for per-cpu counter access).  diskstats access
    should always be enclosed between the two functions.  As such, there's
    no need for the versions which disables preemption.  They're removed
    and double underbars ones are renamed to drop the underbars.  As an
    extra argument is added, there's no danger of using the old version
    disk_stat_lock() uses get_cpu() and returns the cpu index and all
    diskstat functions which access per-cpu counters now has @cpu
    argument to help RT.
    This change adds RCU or preemption operations at some places but also
    collapses several preemption ops into one at others.  Overall, the
    performance difference should be negligible as all involved ops are
    very lightweight per-cpu ones.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
raid0.c 14.1 KB