On Thu, Jun 1, 2017 at 5:26 PM, Yan, Zheng ukernel@gmail.com wrote:
On Thu, Jun 1, 2017 at 6:22 PM, Arnd Bergmann arnd@arndb.de wrote:
On Thu, Jun 1, 2017 at 11:56 AM, Yan, Zheng ukernel@gmail.com wrote:
On Sat, Apr 8, 2017 at 8:57 AM, Deepa Dinamani deepa.kernel@gmail.com wrote:
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index 517838b..77204da 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -1922,7 +1922,7 @@ static void rbd_osd_req_format_write(struct rbd_obj_request *obj_request) { struct ceph_osd_request *osd_req = obj_request->osd_req;
osd_req->r_mtime = CURRENT_TIME;
ktime_get_real_ts(&osd_req->r_mtime); osd_req->r_data_offset = obj_request->offset;}
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c index c681762..1d3fa90 100644 --- a/fs/ceph/mds_client.c +++ b/fs/ceph/mds_client.c @@ -1666,6 +1666,7 @@ struct ceph_mds_request * ceph_mdsc_create_request(struct ceph_mds_client *mdsc, int op, int mode) { struct ceph_mds_request *req = kzalloc(sizeof(*req), GFP_NOFS);
struct timespec ts; if (!req) return ERR_PTR(-ENOMEM);@@ -1684,7 +1685,8 @@ ceph_mdsc_create_request(struct ceph_mds_client *mdsc, int op, int mode) init_completion(&req->r_safe_completion); INIT_LIST_HEAD(&req->r_unsafe_item);
req->r_stamp = current_fs_time(mdsc->fsc->sb);
ktime_get_real_ts(&ts);req->r_stamp = timespec_trunc(ts, mdsc->fsc->sb->s_time_gran);This change causes our kernel_untar_tar test case to fail (inode's ctime goes back). The reason is that there is time drift between the time stamps got by ktime_get_real_ts() and current_time(). We need to revert this change until current_time() uses ktime_get_real_ts() internally.
Hmm, the change was not supposed to have a user-visible effect, so something has gone wrong, but I don't immediately see how it relates to what you observe.
ktime_get_real_ts() and current_time() use the same time base, there is no drift, but there is a difference in resolution, as the latter uses the time stamp of the last jiffies update, which may be up to one jiffy (10ms) behind the exact time we put in the request stamps here.
Do you still see problems if you use current_kernel_time() instead of ktime_get_real_ts()?
The problem disappears after using current_kernel_time().
https://github.com/ceph/ceph-client/commit/2e0f648da23167034a3cf1500bc90ec60...
From the commit above:
"It seems there is time drift between ktime_get_real_ts() and current_kernel_time()"
Its more of a granularity difference. current_kernel_time() returns the cached time at the last tick, where as ktime_get_real_ts() reads the clocksource hardware and returns the immediate time.
Filesystems usually use the cached time (similar to CLOCK_REALTIME_COARSE), for performance reasons, as touching the clocksource takes time.
thanks -john