On 10/13/2014 05:18 AM, Nicheal wrote:
Hi,
I'm currently finding that enable WritebackThrottle lead to lower IOPS
for large number of small io. Since WritebackThrottle calls
fdatasync(fd) to flush an object content to disk, large number of
ramdom small io always cause the WritebackThrottle to submit one or
two 4k io every time.
Thus, it is much slower than the global sync in
FileStore::sync_entry(). Note:: here, I use xfs as the FileStore
underlying filesystem. So I would know that if any impact when I
disable Writeback throttles. I cannot catch the idea on the website
(http://ceph.com/docs/master/dev/osd_internals/wbthrottle/).
Large number of inode will cause longer time to sync, but submitting a
batch of write to disk always faster than submitting few io update to
the disk.
Hi Nichael,
When the wbthrottle code was introduced back around dumpling we had to
increase the sync intervals quite a bit to get it performing similarly
to cuttlefish. Have you tried playing with the various wbthrottle xfs
tuneables to see if you can improve the behaviour?
OPTION(filestore_wbthrottle_enable, OPT_BOOL, true)
OPTION(filestore_wbthrottle_xfs_bytes_start_flusher, OPT_U64, 41943040)
OPTION(filestore_wbthrottle_xfs_bytes_hard_limit, OPT_U64, 419430400)
OPTION(filestore_wbthrottle_xfs_ios_start_flusher, OPT_U64, 500)
OPTION(filestore_wbthrottle_xfs_ios_hard_limit, OPT_U64, 5000)
OPTION(filestore_wbthrottle_xfs_inodes_start_flusher, OPT_U64, 500)
Mark
Nicheal
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