MFC 297219

MFC 297219

    hyperv/vmbus: use a better retry method in hv_vmbus_post_message()

    Most often, hv_vmbus_post_message() doesn't fail.  However, it fails
    intermittently when GPADLs of large shared memory is to be established
    with the host, e.g. on the hn(4) attach path: a GPADL of 15MB sendbuf
    is created, for which lots of messages will be flooded to the host.
    The host side tries to throttle the message rate by returning
    HV_STATUS_INSUFFICIENT_BUFFERS.

    Before this commit, we do several retries for failed messages, but the
    delay between each retry is pretty/too low, which will cause sporadic
    message posting failure.  We now use large delay (>=1ms) between each
    retry to fix the message posting failure.

    Submitted by:       Dexuan Cui <decui microsoft com>
    Reviewed by:        sephe
    MFC after:  1 week
    Sponsored by:       Microsoft OSTC
    Differential Revision:      https://reviews.freebsd.org/D5715

git-svn-id: svn://svn.freebsd.org/base/stable/10@301924 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f