I seem to be having performance issues where certain read system calls take up to three seconds to complete. My test app is bonnie++, and the slow-downs appear to be happen in the "Rewriting" portion of the test, though I'm not sure if this is exclusive. If I watch top and iostat for the device in question, I see activity on the device, then long (up to three second) periods of no apparent I/O. During the periods of no I/O the bonnie++ process is blocked on disk I/O, so it seems that the system it trying to do something. Network traces seem to show that the host machine is not waiting on the RAID array, and the packet following the dead-period seems to always be sent from the host to the coraid device. Unfortunately, I don't know how to dig in any deeper to figure out what the problem is.
Below are strace and tcpdump snippets that show what I'm talking about. Notice the time stamps and the time spent in system calls in <> brackets after the call. I'm quite far from a GFS expert, so please let me know if other data would be helpful.
Any help is much appreciated.
Thanks!
Tom
# tcpdump -s14 -n
...
23:46:40.382119 00:30:48:8b:2b:47 > 00:30:48:57:a7:ed, ethertype Unknown (0x88a2), length 4132:
23:46:40.382131 00:30:48:8b:2b:47 > 00:30:48:57:a7:ed, ethertype Unknown (0x88a2), length 4132:
23:46:43.406173 00:30:48:57:a7:ed > 00:30:48:8b:2b:47, ethertype Unknown (0x88a2), length 60:
23:46:43.406495 00:30:48:8b:2b:47 > 00:30:48:57:a7:ed, ethertype Unknown (0x88a2), length 4132:
23:46:43.406502 00:30:48:8b:2b:47 > 00:30:48:57:a7:ed, ethertype Unknown (0x88a2), length 1060:
# strace -p 19845 -T -tt -s 5c
...
23:46:40.380764 write(15, "\301"..., 8192) = 8192 <0.000024>
23:46:40.380814 read(15, "\301"..., 8192) = 8192 <3.026205>
23:46:43.407054 lseek(15, 3899392, SEEK_SET) = 3899392 < 0.000006>
23:46:43.407090 write(15, "\301"..., 8192) = 8192 <0.000032>
[root@gfs03 ~]# gfs_tool counters /opt/coraid
locks 6651
locks held 6585
incore inodes 69
metadata buffers 2519
unlinked inodes 0
quota IDs 0
incore log buffers 1
log space used 0.20%
meta header cache entries 0
glock dependencies 0
glocks on reclaim list 0
log wraps 5
outstanding LM calls 0
outstanding BIO calls 1
fh2dentry misses 0
glocks reclaimed 755
glock nq calls 104485385
glock dq calls 104426553
glock prefetch calls 1
lm_lock calls 73715
lm_unlock calls 651
lm callbacks 81471
address operations 112591696
dentry operations 257
export operations 0
file operations 29841238
inode operations 1929
super operations 28201660
vm operations 0
block I/O reads 3448075
block I/O writes 36719795
[root@gfs03 ~]# gfs_tool gettune /opt/coraid
ilimit1 = 100
ilimit1_tries = 3
ilimit1_min = 1
ilimit2 = 500
ilimit2_tries = 10
ilimit2_min = 3
demote_secs = 300
incore_log_blocks = 1024
jindex_refresh_secs = 60
depend_secs = 60
scand_secs = 5
recoverd_secs = 60
logd_secs = 1
quotad_secs = 5
inoded_secs = 15
quota_simul_sync = 64
quota_warn_period = 10
atime_quantum = 3600
quota_quantum = 60
quota_scale = 1.0000 (1, 1)
quota_enforce = 1
quota_account = 1
new_files_jdata = 0
new_files_directio = 0
max_atomic_write = 4194304
max_readahead = 262144
lockdump_size = 131072
stall_secs = 600
complain_secs = 10
reclaim_limit = 5000
entries_per_readdir = 32
prefetch_secs = 10
statfs_slots = 64
max_mhc = 10000
greedy_default = 100
greedy_quantum = 25
greedy_max = 250
rgrp_try_threshold = 100
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