On 2010-02-01, at 15:36, Eric Sandeen wrote:
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.
Since these are on-demand loads, one option is when the current group
is ~80% full submit an async read for the next group bitmap so that it
will be in memory by the next time we need it.
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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