md/raid10: prevent unnecessary calls to wake_up() in fast path

mainline inclusion
from md-next
commit 7fdc91928ac109d3d1468ad7f951deb29a375e3d
category: performance
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I5PRMO
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/song/md.git/commit/?h=md-next&id=7fdc91928ac109d3d1468ad7f951deb29a375e3d



--------------------------------

Currently, wake_up() is called unconditionally in fast path such as
raid10_make_request(), which will cause lock contention under high
concurrency:

raid10_make_request
 wake_up
  __wake_up_common_lock
   spin_lock_irqsave

Improve performance by only call wake_up() if waitqueue is not empty.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Signed-off-by: Song Liu <song@kernel.org>
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>