[LU-9782] High CPU usage with random IO test.

Related — Thu, 26 Oct 2017 16:50:46 +0000

osd-ldiskfs have a several osd_is_mapped calls when extent tree scanned to get decission about error for rewrite case. But extent tree is huge with while random io write test and search is CPU expensive in this case. typical perf output is

|--75.99%-- rb_next
            |          |          
            |          |--94.49%-- ldiskfs_es_find_delayed_extent_range
            |          |          ldiskfs_fiemap
            |          |          osd_is_mapped
            |          |          osd_declare_write_commit
            |          |          ofd_commitrw_write.isra.32
            |          |          ofd_commitrw
            |          |          obd_commitrw.constprop.39
            |          |          tgt_brw_write
            |          |          tgt_request_handle
            |          |          ptlrpc_server_handle_request
            |          |          ptlrpc_main
            |          |          kthread
            |          |          ret_from_fork
            |          |          
            |          |--5.49%-- ldiskfs_fiemap
            |          |          osd_is_mapped
            |          |          osd_declare_write_commit
            |          |          ofd_commitrw_write.isra.32
            |          |          ofd_commitrw
            |          |          obd_commitrw.constprop.39
            |          |          tgt_brw_write
            |          |          tgt_request_handle
            |          |          ptlrpc_server_handle_request
            |          |          ptlrpc_main
            |          |          kthread
            |          |          ret_from_fork
            |           --0.02%-- [...]
            |          
            |--21.80%-- ldiskfs_es_find_delayed_extent_range
            |          |          
            |          |--100.00%-- ldiskfs_fiemap
            |          |          osd_is_mapped
            |          |          osd_declare_write_commit
            |          |          ofd_commitrw_write.isra.32
            |          |          ofd_commitrw
            |          |          obd_commitrw.constprop.39
            |          |          tgt_brw_write
            |          |          tgt_request_handle
            |          |          ptlrpc_server_handle_request
            |          |          ptlrpc_main
            |          |          kthread
            |          |          ret_from_fork
            |           --0.00%-- [...]

avoid second search by caching result on hight bits of lnb_flags which not used in wire increase a performance dramatically

without patch with default mkfsoptions: CPU usage 100% with 55-60K random 4K writes
with the patch: CPU usage 50-60% with 250K random 4K writes

Whamcloud Community JIRA

[LU-9782] High CPU usage with random IO test.