[gpfsug-discuss] Poor client performance with high cpu usage of mmfsd process

Fri Nov 13 09:21:17 GMT 2020

Hi, Kamil, 
looks your tracefile setting has been too low: 
all streams included Thu Nov 12 20:58:19.950515266 2020 (TOD 
1605232699.950515, cycles 20701552715873212) <---- useful part of trace 
extends from here
trace quiesced Thu Nov 12 20:58:20.133134000 2020 (TOD 1605232700.000133, 
cycles 20701553190681534) <---- to here
means you effectively captured a period of about 5ms only ... you can't 
see much from that. 

I'd assumed the default trace file size would be sufficient here but it 
doesn't seem to. 
try running with something like 
 mmtracectl --start --trace-file-size=512M --trace=io 
--tracedev-write-mode=overwrite -N <your_critical_node>. 

However, if you say "no major waiter" - how many waiters did you see at 
any time? what kind of waiters were the oldest, how long they'd waited?
it could indeed well be that some job is just creating a killer workload. 

The very short cyle time of the trace points, OTOH, to high activity, OTOH 
the trace file setting appears quite low (trace=io doesnt' collect many 
trace infos, just basic IO stuff). 
If I might ask: what version of GPFS are you running?

Mit freundlichen Grüßen / Kind regards

Dr. Uwe Falke
IT Specialist
Hybrid Cloud Infrastructure / Technology Consulting & Implementation 
Services
+49 175 575 2877 Mobile
Rathausstr. 7, 09111 Chemnitz, Germany
uwefalke at de.ibm.com

IBM Services

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From:   "Czauz, Kamil" <Kamil.Czauz at Squarepoint-Capital.com>
To:     gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date:   13/11/2020 03:33
Subject:        [EXTERNAL] Re: [gpfsug-discuss] Poor client performance 
with high cpu usage     of      mmfsd process
Sent by:        gpfsug-discuss-bounces at spectrumscale.org

Hi Uwe -

I hit the issue again today, no major waiters, and nothing useful from the 
iohist report. Nothing interesting in the logs either.

I was able to get a trace today while the issue was happening. I took 2 
traces a few min apart.

The beginning of the traces look something like this:
Overwrite trace parameters:
buffer size: 134217728
64 kernel trace streams, indices 0-63 (selected by low bits of processor 
ID)
128 daemon trace streams, indices 64-191 (selected by low bits of thread 
ID)
Interval for calibrating clock rate was 100.019054 seconds and 
260049296314 cycles
Measured cycle count update rate to be 2599997559 per second <---- using 
this value
OS reported cycle count update rate as 2599999000 per second
Trace milestones:
kernel trace enabled Thu Nov 12 20:56:40.114080000 2020 (TOD 
1605232600.114080, cycles 20701293141385220)
daemon trace enabled Thu Nov 12 20:56:40.247430000 2020 (TOD 
1605232600.247430, cycles 20701293488095152)
all streams included Thu Nov 12 20:58:19.950515266 2020 (TOD 
1605232699.950515, cycles 20701552715873212) <---- useful part of trace 
extends from here
trace quiesced Thu Nov 12 20:58:20.133134000 2020 (TOD 1605232700.000133, 
cycles 20701553190681534) <---- to here
Approximate number of times the trace buffer was filled: 553.529

Here is the output of
trsum.awk details=0
I'm not quite sure what to make of it, can you help me decipher it? The 
'lookup' operations are taking a hell of a long time, what does that mean?

Capture 1

Unfinished operations:

21234 ***************** lookup ************** 0.165851604
290020 ***************** lookup ************** 0.151032241
302757 ***************** lookup ************** 0.168723402
301677 ***************** lookup ************** 0.070016530
230983 ***************** lookup ************** 0.127699082
21233 ***************** lookup ************** 0.060357257
309046 ***************** lookup ************** 0.157124551
301643 ***************** lookup ************** 0.165543982
304042 ***************** lookup ************** 0.172513838
167794 ***************** lookup ************** 0.056056815
189680 ***************** lookup ************** 0.062022237
362216 ***************** lookup ************** 0.072063619
406314 ***************** lookup ************** 0.114121838
167776 ***************** lookup ************** 0.114899642
303016 ***************** lookup ************** 0.144491120
290021 ***************** lookup ************** 0.142311603
167762 ***************** lookup ************** 0.144240366
248530 ***************** lookup ************** 0.168728131
0 0.000000000 ********* Unfinished IO: buffer/disk 30018014000 
14:48493092752^\00000000FFFFFFFF
0 0.000000000 ********* Unfinished IO: buffer/disk 30018014000 
14:48493092752^\FFFFFFFE
0 0.000000000 ********* Unfinished IO: buffer/disk 2000006B000 
2:6058336^\00000000FFFFFFFF
0 0.000000000 ********* Unfinished IO: buffer/disk 30018014000 
14:48493092752^\FFFFFFFF
0 0.000000000 ********* Unfinished IO: buffer/disk 2000006B000 
2:6058336^\FFFFFFFE
0 0.000000000 ********* Unfinished IO: buffer/disk 2000006B000 
2:6058336^\FFFFFFFF
0 0.000000000 ********* Unfinished IO: buffer/disk 3000002E000 
2:1917676744^\FFFFFFFE
0 0.000000000 ********* Unfinished IO: buffer/disk 3000002E000 
2:1917676744^\00000000FFFFFFFF
0 0.000000000 ********* Unfinished IO: buffer/disk 3000002E000 
2:1917676744^\FFFFFFFF

Elapsed trace time: 0.182617894 seconds
Elapsed trace time from first VFS call to last: 0.182617893
Time idle between VFS calls: 0.000006317 seconds

Operations stats: total time(s) count avg-usecs wait-time(s) avg-usecs
rdwr 0.012021696 35 343.477
read_inode2 0.000100787 43 2.344
follow_link 0.000050609 8 6.326
pagein 0.000097806 10 9.781
revalidate 0.000010884 156 0.070
open 0.001001824 18 55.657
lookup 1.152449696 36 32012.492
delete_inode 0.000036816 38 0.969
permission 0.000080574 14 5.755
release 0.000470096 18 26.116
mmap 0.000340095 9 37.788
llseek 0.000001903 9 0.211

User thread stats: GPFS-time(sec) Appl-time GPFS-% Appl-% Ops
221919 0.000000244 0.050064080 0.00% 100.00% 4
167794 0.000011891 0.000069707 14.57% 85.43% 4
309046 0.147664569 0.000074663 99.95% 0.05% 9
349767 0.000000070 0.000000000 100.00% 0.00% 1
301677 0.017638372 0.048741086 26.57% 73.43% 12
84407 0.000010448 0.000016977 38.10% 61.90% 3
406314 0.000002279 0.000122367 1.83% 98.17% 7
25464 0.043270937 0.000006200 99.99% 0.01% 2
362216 0.000005617 0.000017498 24.30% 75.70% 2
379982 0.000000626 0.000000000 100.00% 0.00% 1
230983 0.123947465 0.000056796 99.95% 0.05% 6
21233 0.047877661 0.004887113 90.74% 9.26% 17
302757 0.154486003 0.010695642 93.52% 6.48% 24
248530 0.000006763 0.000035442 16.02% 83.98% 3
303016 0.014678039 0.000013098 99.91% 0.09% 2
301643 0.088025575 0.054036566 61.96% 38.04% 33
3339 0.000034997 0.178199426 0.02% 99.98% 35
21234 0.164240073 0.000262711 99.84% 0.16% 39
167762 0.000011886 0.000041865 22.11% 77.89% 3
336006 0.000001246 0.100519562 0.00% 100.00% 16
304042 0.121322325 0.019218406 86.33% 13.67% 33
301644 0.054325242 0.087715613 38.25% 61.75% 37
301680 0.000015005 0.020838281 0.07% 99.93% 9
290020 0.147713357 0.000121422 99.92% 0.08% 19
290021 0.000476072 0.000085833 84.72% 15.28% 10
44777 0.040819757 0.000010957 99.97% 0.03% 3
189680 0.000000044 0.000002376 1.82% 98.18% 1
241759 0.000000698 0.000000000 100.00% 0.00% 1
184839 0.000001621 0.150341986 0.00% 100.00% 28
362220 0.000010818 0.000020949 34.05% 65.95% 2
104687 0.000000495 0.000000000 100.00% 0.00% 1

# total App-read/write = 45 Average duration = 0.000269322 sec
# time(sec) count % %ile read write avgBytesR avgBytesW
0.000500 34 0.755556 0.755556 34 0 32889 0
0.001000 10 0.222222 0.977778 10 0 108136 0
0.004000 1 0.022222 1.000000 1 0 8 0

# max concurrant App-read/write = 2
# conc count % %ile
1 38 0.844444 0.844444
2 7 0.155556 1.000000

Capture 2

Unfinished operations:

335096 ***************** lookup ************** 0.289127895
334691 ***************** lookup ************** 0.225380797
362246 ***************** lookup ************** 0.052106493
334694 ***************** lookup ************** 0.048567769
362220 ***************** lookup ************** 0.054825580
333972 ***************** lookup ************** 0.275355791
406314 ***************** lookup ************** 0.283219905
334686 ***************** lookup ************** 0.285973208
289606 ***************** lookup ************** 0.064608288
21233 ***************** lookup ************** 0.074923689
189680 ***************** lookup ************** 0.089702578
335100 ***************** lookup ************** 0.151553955
334685 ***************** lookup ************** 0.117808430
167700 ***************** lookup ************** 0.119441314
336813 ***************** lookup ************** 0.120572137
334684 ***************** lookup ************** 0.124718126
21234 ***************** lookup ************** 0.131124745
84407 ***************** lookup ************** 0.132442945
334696 ***************** lookup ************** 0.140938740
335094 ***************** lookup ************** 0.201637910
167735 ***************** lookup ************** 0.164059859
334687 ***************** lookup ************** 0.252930745
334695 ***************** lookup ************** 0.278037098
341818 0.291815990 ********* Unfinished IO: buffer/disk 50000015000 
3:439888512^\scratch_metadata_5
341818 0.291822084 MSG FSnd: nsdMsgReadExt msg_id 2894690129 Sduration 
199.688 + us
100041 0.025061905 MSG FRep: nsdMsgReadExt msg_id 1012644746 Rduration 
266959.867 us Rlen 0 Hduration 266963.954 + us

Elapsed trace time: 0.292021772 seconds
Elapsed trace time from first VFS call to last: 0.292021771
Time idle between VFS calls: 0.001436519 seconds

Operations stats: total time(s) count avg-usecs wait-time(s) avg-usecs
rdwr 0.000831801 4 207.950
read_inode2 0.000082347 31 2.656
pagein 0.000033905 3 11.302
revalidate 0.000013109 156 0.084
open 0.000237969 22 10.817
lookup 1.233407280 10 123340.728
delete_inode 0.000013877 33 0.421
permission 0.000046486 8 5.811
release 0.000172456 21 8.212
mmap 0.000064411 2 32.206
llseek 0.000000391 2 0.196
readdir 0.000213657 36 5.935

User thread stats: GPFS-time(sec) Appl-time GPFS-% Appl-% Ops
335094 0.053506265 0.000170270 99.68% 0.32% 16
167700 0.000008522 0.000027547 23.63% 76.37% 2
167776 0.000008293 0.000019462 29.88% 70.12% 2
334684 0.000023562 0.000160872 12.78% 87.22% 8
349767 0.000000467 0.250029787 0.00% 100.00% 5
84407 0.000000230 0.000017947 1.27% 98.73% 2
334685 0.000028543 0.000094147 23.26% 76.74% 8
406314 0.221755229 0.000009720 100.00% 0.00% 2
334694 0.000024913 0.000125229 16.59% 83.41% 10
335096 0.254359005 0.000240785 99.91% 0.09% 18
334695 0.000028966 0.000127823 18.47% 81.53% 10
334686 0.223770082 0.000267271 99.88% 0.12% 24
334687 0.000031265 0.000132905 19.04% 80.96% 9
334696 0.000033808 0.000131131 20.50% 79.50% 9
129075 0.000000102 0.000000000 100.00% 0.00% 1
341842 0.000000318 0.000000000 100.00% 0.00% 1
335100 0.059518133 0.000287934 99.52% 0.48% 19
224423 0.000000471 0.000000000 100.00% 0.00% 1
336812 0.000042720 0.000193294 18.10% 81.90% 10
21233 0.000556984 0.000083399 86.98% 13.02% 11
289606 0.000000088 0.000018043 0.49% 99.51% 2
362246 0.014440188 0.000046516 99.68% 0.32% 4
21234 0.000524848 0.000162353 76.37% 23.63% 13
336813 0.000046426 0.000175666 20.90% 79.10% 9
3339 0.000011816 0.272396876 0.00% 100.00% 29
341818 0.000000778 0.000000000 100.00% 0.00% 1
167735 0.000007866 0.000049468 13.72% 86.28% 3
175480 0.000000278 0.000000000 100.00% 0.00% 1
336006 0.000001170 0.250020470 0.00% 100.00% 16
44777 0.000000367 0.250149757 0.00% 100.00% 6
189680 0.000002717 0.000006518 29.42% 70.58% 1
184839 0.000003001 0.250144214 0.00% 100.00% 35
145858 0.000000687 0.000000000 100.00% 0.00% 1
333972 0.218656404 0.000043897 99.98% 0.02% 4
334691 0.187695040 0.000295117 99.84% 0.16% 25

# total App-read/write = 7 Average duration = 0.000123672 sec
# time(sec) count % %ile read write avgBytesR avgBytesW
0.000500 7 1.000000 1.000000 7 0 1172 0

-----Original Message-----
From: gpfsug-discuss-bounces at spectrumscale.org 
<gpfsug-discuss-bounces at spectrumscale.org> On Behalf Of Uwe Falke
Sent: Wednesday, November 11, 2020 8:57 PM
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Subject: Re: [gpfsug-discuss] Poor client performance with high cpu usage 
of mmfsd process

Hi, Kamil,
I suppose you'd rather not see such an issue than pursue the ugly 
work-around to kill off processes.
In such situations, the first looks should be for the GPFS log (on the 
client, on the cluster manager, and maybe on the file system manager) and 
for the current waiters (that is the list of currently waiting threads) on 
the hanging client.

-> /var/adm/ras/mmfs.log.latest
mmdiag --waiters

That might give you a first idea what is taking long and which components 
are involved.

Also,
mmdiag --iohist
shows you the last IOs and some stats (service time, size) for them.

Either that clue is already sufficient, or you go on (if you see DIO 
somewhere, direct IO is used which might slow down things, for example).
GPFS has a nice tracing which you can configure or just run the default 
trace.

Running a dedicated (low-level) io trace can be achieved by mmtracectl 
--start --trace=io --tracedev-write-mode=overwrite -N <your_critical_node> 
then, when the issue is seen, stop the trace by
mmtracectl --stop -N <your_critical_node>

Do not wait to stop the trace once you've seen the issue, the trace file 
cyclically overwrites its output. If the issue lasts some time you could 
also start the trace while you see it, run the trace for say 20 secs and 
stop again. On stopping the trace, the output gets converted into an ASCII 
trace file named trcrpt.*(usually in /tmp/mmfs, check the command output).

There you should see lines with FIO which carry the inode of the related 
file after the "tag" keyword.
example:
0.000745100 25123 TRACE_IO: FIO: read data tag 248415 43466 ioVecSize 8 
1st buf 0x299E89BC000 disk 8D0 da 154:2083875440 nSectors 128 err 0 
finishTime 1563473283.135212150

-> inode is 248415

there is a utility , tsfindinode, to translate that into the file path.
you need to build this first if not yet done:
cd /usr/lpp/mmfs/samples/util ; make
, then run
./tsfindinode -i <inode_num> <fs_mount_point>

For the IO trace analysis there is an older tool :
/usr/lpp/mmfs/samples/debugtools/trsum.awk.

Then there is some new stuff I've not yet used in 
/usr/lpp/mmfs/samples/traceanz/ (always check the README)

Hope that halps a bit.

Mit freundlichen Grüßen / Kind regards

Dr. Uwe Falke
IT Specialist
Hybrid Cloud Infrastructure / Technology Consulting & Implementation 
Services
+49 175 575 2877 Mobile
Rathausstr. 7, 09111 Chemnitz, Germany
uwefalke at de.ibm.com

IBM Services

IBM Data Privacy Statement

IBM Deutschland Business & Technology Services GmbH
Geschäftsführung: Sven Schooss, Stefan Hierl Sitz der Gesellschaft: 
Ehningen
Registergericht: Amtsgericht Stuttgart, HRB 17122

From: "Czauz, Kamil" <Kamil.Czauz at Squarepoint-Capital.com>
To: "gpfsug-discuss at spectrumscale.org"
<gpfsug-discuss at spectrumscale.org>
Date: 11/11/2020 23:36
Subject: [EXTERNAL] [gpfsug-discuss] Poor client performance with
high cpu usage of mmfsd process
Sent by: gpfsug-discuss-bounces at spectrumscale.org

We regularly run into performance issues on our clients where the client 
seems to hang when accessing any gpfs mount, even something simple like a
ls could take a few minutes to complete. This affects every gpfs mount
on the client, but other clients are working just fine. Also the mmfsd 
process at this point is spinning at something like 300-500% cpu.

The only way I have found to solve this is by killing processes that may 
be doing heavy i/o to the gpfs mounts - but this is more of an art than a 
science. I often end up killing many processes before finding the 
offending one.

My question is really about finding the offending process easier. Is there 
something similar to iotop or a trace that I can enable that can tell me 
what files/processes and being heavily used by the mmfsd process on the 
client?

-Kamil
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