[gpfsug-discuss] Poor client performance with high cpu usage of mmfsd process
Uwe Falke
UWEFALKE at de.ibm.com
Thu Nov 12 01:56:46 GMT 2020
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
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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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