Description of problem:
-----------------------

After upgrading the cluster from 7.1z1 to 8.0, and triggered a snapshot sync as part of cephfs mirroring. The sync duration of the new snapshots is not proper and shows an invalid value whereas the sync was completed in 4-5 sec.


Peer Status on 7.z1 Version : 
-----------------------------

Deleted a file and created a snapshot on the subvolume which was part of mirroring : 

[root@magna029 d_000]# rm -rf _magna029_00_95_

[root@magna029 d_000]# ceph fs subvolume snapshot create cephfs2 subvolc2_2 snap_svc2_2_file_remove

[root@magna028 26171d20-f1d5-11ee-b6c2-002590fc2a2e]# ceph --admin-daemon ceph-client.cephfs-mirror.magna028.kxaogg.2.94766774573344.asok fs mirror peer status cephfs2@4 224de958-5b2c-4459-805c-79fca9752835
{
    "/volumes/_nogroup/subvolc2_2": {
        "state": "idle",
        "last_synced_snap": {
            "id": 11,
            "name": "snap_svc2_2_file_remove",
            "sync_duration": 44.572015217000001,
            "sync_time_stamp": "363647.856055s"
        },
        "snaps_synced": 5,
        "snaps_deleted": 0,
        "snaps_renamed": 0
    }
}

It took 44.57 sec to sync to the remote cluster.

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

Upgraded the cluster to 8.0: 
==========================
Repeated the same test on 8.0 build - ceph version 19.1.0-55.el9cp

[root@magna029 d_099]# ls _magna029_00_9944_
_magna029_00_9944_

[root@magna029 d_099]# rm -rf _magna029_00_9944_

[root@magna029 d_099]# ls _magna029_00_9944_
ls: cannot access '_magna029_00_9944_': No such file or directory

[root@magna029 d_099]# ceph fs subvolume snapshot create cephfs2 subvolc2_2 snap_svc2_2_new_file_delete


[root@magna028 26171d20-f1d5-11ee-b6c2-002590fc2a2e]# ceph --admin-daemon ceph-client.cephfs-mirror.magna028.kxaogg.2.93988612716904.asok fs mirror peer status cephfs2@4 224de958-5b2c-4459-805c-79fca9752835
{
    "/volumes/_nogroup/subvolc2_2": {
        "state": "idle",
        "last_synced_snap": {
            "id": 15,
            "name": "snap_svc2_2_new_file_delete",
            "sync_duration": 6831,
            "sync_time_stamp": "367396.355202s",
            "sync_bytes": 0
        },
        "snaps_synced": 4,
        "snaps_deleted": 0,
        "snaps_renamed": 0
    }
}

---
The last sync duration is incorrectly showing as 6831 seconds, even though the sync actually completed in 4-5 seconds.