Eric Sandeen wrote: > So uninit_bg doesn't seem to help. (this was on 2.6.32-ish) > > some oprofiling may be in order ... Or stapping ... thanks to hints from the stap guys, using a modified version of http://sourceware.org/systemtap/examples/profiling/fntimes.stp I printed out function times higher than avg and correlated to writes above average from the testcase (cleaned up manually a bit): 1265062212927230 function ext4_mb_load_buddy well over average time (42303 vs 2) 1265062212927399 function ext4_mb_regular_allocator well over average time (42476 vs 5495) 1265062212949252 function ext4_mb_mark_diskspace_used well over average time (21739 vs 196) 1265062212949306 function ext4_mb_new_blocks well over average time (64738 vs 2457) 1265062212949647 function ext4_ext_get_blocks well over average time (65211 vs 1106) 1265062212949678 function ext4_get_blocks well over average time (65357 vs 1844) 1265062212949695 function ext4_get_block well over average time (65479 vs 683) 1265062212951284 function ext4_ind_direct_IO well over average time (68891 vs 3034) 1265062212951299 function ext4_direct_IO well over average time (68908 vs 3046) 1265062212951497 function ext4_file_write well over average time (69437 vs 3590) 1265062212951534 size 134470144 time 69477310 avg 3601820 Unfortunately under ext4_mb_load_buddy is a lot of static/inlined functions so no more detailed info yet. But loading the buddy bitmap for a new group seems to be the big hitter here - I'll keep digging, or maybe Aneesh, who groks mballoc better than I do (I think) might have an idea. But yeah, writes randomly taking 20x longer than usual sounds bad. :( -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
