[gpfsug-discuss] bizarre performance behavior
Kumaran Rajaram
kums at us.ibm.com
Thu May 4 23:22:12 BST 2017
Hi,
>>So the problem was some bad ib routing. We changed some ib links, and
then we got also 12GB/s read with nsdperf.
>>On our clients we then are able to achieve the 7,2GB/s in total we also
saw using the nsd servers!
This is good to hear.
>> We are now running some tests with different blocksizes and parameters,
because our backend storage is able to do more than the 7.2GB/s we get
with GPFS (more like 14GB/s in total). I guess prefetchthreads and
nsdworkerthreads are the ones to look at?
If you are on 4.2.0.3 or higher, you can use workerThreads config paramter
(start with value of 128, and increase in increments of 128 until MAX
supported) and this setting will auto adjust values for other parameters
such as prefetchThreads, worker3Threads etc.
https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki/General%20Parallel%20File%20System%20%28GPFS%29/page/Tuning%20Parameters
In addition to trying larger file-system block-size (e.g. 4MiB or higher
such that is aligns with storage volume RAID-stripe-width) and config
parameters (e.g , workerThreads, ignorePrefetchLUNCount), it will be good
to assess the "backend storage" performance for random I/O access pattern
(with block I/O sizes in units of FS block-size) as this is more likely
I/O scenario that the backend storage will experience when you have many
GPFS nodes performing I/O simultaneously to the file-system (in production
environment).
mmcrfs has option "[-j {cluster | scatter}]". "-j scatter" would be
recommended for consistent file-system performance over the lifetime of
the file-system but then "-j scatter" will result in random I/O to
backend storage (even though application is performing sequential I/O).
For your test purposes, you may assess the GPFS file-system performance by
mmcrfs with "-j cluster" and you may see good sequential results (compared
to -j scatter) for lower client counts but as you scale the client counts
the combined workload can result in "-j scatter" to backend storage
(limiting the FS performance to random I/O performance of the backend
storage).
[snip from mmcrfs]
layoutMap={scatter | cluster}
Specifies the block allocation map type. When
allocating blocks for a given file, GPFS first
uses a round‐robin algorithm to spread the data
across all disks in the storage pool. After a
disk is selected, the location of the data
block on the disk is determined by the block
allocation map type. If cluster is
specified, GPFS attempts to allocate blocks in
clusters. Blocks that belong to a particular
file are kept adjacent to each other within
each cluster. If scatter is specified,
the location of the block is chosen randomly.
The cluster allocation method may provide
better disk performance for some disk
subsystems in relatively small installations.
The benefits of clustered block allocation
diminish when the number of nodes in the
cluster or the number of disks in a file system
increases, or when the file system’s free space
becomes fragmented. The cluster
allocation method is the default for GPFS
clusters with eight or fewer nodes and for file
systems with eight or fewer disks.
The scatter allocation method provides
more consistent file system performance by
averaging out performance variations due to
block location (for many disk subsystems, the
location of the data relative to the disk edge
has a substantial effect on performance). This
allocation method is appropriate in most cases
and is the default for GPFS clusters with more
than eight nodes or file systems with more than
eight disks.
The block allocation map type cannot be changed
after the storage pool has been created.
..
..
-j {cluster | scatter}
Specifies the default block allocation map type to be
used if layoutMap is not specified for a given
storage pool.
[/snip from mmcrfs]
My two cents,
-Kums
From: Kenneth Waegeman <kenneth.waegeman at ugent.be>
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: 05/04/2017 09:23 AM
Subject: Re: [gpfsug-discuss] bizarre performance behavior
Sent by: gpfsug-discuss-bounces at spectrumscale.org
Hi,
We found out using ib_read_bw and ib_write_bw that there were some links
between server and clients degraded, having a bandwith of 350MB/s
strangely, nsdperf did not report the same. It reported 12GB/s write and
9GB/s read, which was much more then we actually could achieve.
So the problem was some bad ib routing. We changed some ib links, and then
we got also 12GB/s read with nsdperf.
On our clients we then are able to achieve the 7,2GB/s in total we also
saw using the nsd servers!
Many thanks for the help !!
We are now running some tests with different blocksizes and parameters,
because our backend storage is able to do more than the 7.2GB/s we get
with GPFS (more like 14GB/s in total). I guess prefetchthreads and
nsdworkerthreads are the ones to look at?
Cheers!
Kenneth
On 21/04/17 22:27, Kumaran Rajaram wrote:
Hi Kenneth,
As it was mentioned earlier, it will be good to first verify the raw
network performance between the NSD client and NSD server using the
nsdperf tool that is built with RDMA support.
g++ -O2 -DRDMA -o nsdperf -lpthread -lrt -libverbs -lrdmacm nsdperf.C
In addition, since you have 2 x NSD servers it will be good to perform NSD
client file-system performance test with just single NSD server
(mmshutdown the other server, assuming all the NSDs have primary, server
NSD server configured + Quorum will be intact when a NSD server is brought
down) to see if it helps to improve the read performance + if there are
variations in the file-system read bandwidth results between NSD_server#1
'active' vs. NSD_server #2 'active' (with other NSD server in GPFS "down"
state). If there is significant variation, it can help to isolate the
issue to particular NSD server (HW or IB issue?).
You can issue "mmdiag --waiters" on NSD client as well as NSD servers
during your dd test, to verify if there are unsual long GPFS waiters. In
addition, you may issue Linux "perf top -z" command on the GPFS node to
see if there is high CPU usage by any particular call/event (for e.g., If
GPFS config parameter verbsRdmaMaxSendBytes has been set to low value
from the default 16M, then it can cause RDMA completion threads to go CPU
bound ). Please verify some performance scenarios detailed in Chapter 22
in Spectrum Scale Problem Determination Guide (link below).
https://www.ibm.com/support/knowledgecenter/en/STXKQY_4.2.3/com.ibm.spectrum.scale.v4r23.doc/pdf/scale_pdg.pdf?view=kc
Thanks,
-Kums
From: Kenneth Waegeman <kenneth.waegeman at ugent.be>
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: 04/21/2017 11:43 AM
Subject: Re: [gpfsug-discuss] bizarre performance behavior
Sent by: gpfsug-discuss-bounces at spectrumscale.org
Hi,
We already verified this on our nsds:
[root at nsd00 ~]# /opt/dell/toolkit/bin/syscfg --QpiSpeed
QpiSpeed=maxdatarate
[root at nsd00 ~]# /opt/dell/toolkit/bin/syscfg --turbomode
turbomode=enable
[root at nsd00 ~]# /opt/dell/toolkit/bin/syscfg ‐-SysProfile
SysProfile=perfoptimized
so sadly this is not the issue.
Also the output of the verbs commands look ok, there are connections from
the client to the nsds are there is data being read and writen.
Thanks again!
Kenneth
On 21/04/17 16:01, Kumaran Rajaram wrote:
Hi,
Try enabling the following in the BIOS of the NSD servers (screen shots
below)
Turbo Mode - Enable
QPI Link Frequency - Max Performance
Operating Mode - Maximum Performance
>>>>While we have even better performance with sequential reads on raw
storage LUNS, using GPFS we can only reach 1GB/s in total (each nsd server
seems limited by 0,5GB/s) independent of the number of clients
>>We are testing from 2 testing machines connected to the nsds with
infiniband, verbs enabled.
Also, It will be good to verify that all the GPFS nodes have Verbs RDMA
started using "mmfsadm test verbs status" and that the NSD client-server
communication from client to server during "dd" is actually using Verbs
RDMA using "mmfsadm test verbs conn" command (on NSD client doing dd). If
not, then GPFS might be using TCP/IP network over which the cluster is
configured impacting performance (If this is the case, GPFS
mmfs.log.latest for any Verbs RDMA related errors and resolve).
Regards,
-Kums
From: "Knister, Aaron S. (GSFC-606.2)[COMPUTER SCIENCE CORP]"
<aaron.s.knister at nasa.gov>
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: 04/21/2017 09:11 AM
Subject: Re: [gpfsug-discuss] bizarre performance behavior
Sent by: gpfsug-discuss-bounces at spectrumscale.org
Fantastic news! It might also be worth running "cpupower monitor" or
"turbostat" on your NSD servers while you're running dd tests from the
clients to see what CPU frequency your cores are actually running at.
A typical NSD server workload (especially with IB verbs and for reads) can
be pretty light on CPU which might not prompt your CPU crew governor to up
the frequency (which can affect throughout). If your frequency scaling
governor isn't kicking up the frequency of your CPUs I've seen that cause
this behavior in my testing.
-Aaron
On April 21, 2017 at 05:43:40 EDT, Kenneth Waegeman
<kenneth.waegeman at ugent.be>wrote:
Hi,
We are running a test setup with 2 NSD Servers backed by 4 Dell
Powervaults MD3460s. nsd00 is primary serving LUNS of controller A of the
4 powervaults, nsd02 is primary serving LUNS of controller B.
We are testing from 2 testing machines connected to the nsds with
infiniband, verbs enabled.
When we do dd from the NSD servers, we see indeed performance going to
5.8GB/s for one nsd, 7.2GB/s for the two! So it looks like GPFS is able to
get the data at a decent speed. Since we can write from the clients at a
good speed, I didn't suspect the communication between clients and nsds
being the issue, especially since total performance stays the same using 1
or multiple clients.
I'll use the nsdperf tool to see if we can find anything,
thanks!
K
On 20/04/17 17:04, Knister, Aaron S. (GSFC-606.2)[COMPUTER SCIENCE CORP]
wrote:
Interesting. Could you share a little more about your architecture? Is it
possible to mount the fs on an NSD server and do some dd's from the fs on
the NSD server? If that gives you decent performance perhaps try NSDPERF
next
https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki/General+Parallel+File+System+(GPFS)/page/Testing+network+performance+with+nsdperf
-Aaron
On April 20, 2017 at 10:53:47 EDT, Kenneth Waegeman
<kenneth.waegeman at ugent.be>wrote:
Hi,
Having an issue that looks the same as this one:
We can do sequential writes to the filesystem at 7,8 GB/s total , which is
the expected speed for our current storage
backend. While we have even better performance with sequential reads on
raw storage LUNS, using GPFS we can only reach 1GB/s in total (each nsd
server seems limited by 0,5GB/s) independent of the number of clients
(1,2,4,..) or ways we tested (fio,dd). We played with blockdev params,
MaxMBps, PrefetchThreads, hyperthreading, c1e/cstates, .. as discussed in
this thread, but nothing seems to impact this read performance.
Any ideas?
Thanks!
Kenneth
On 17/02/17 19:29, Jan-Frode Myklebust wrote:
I just had a similar experience from a sandisk infiniflash system
SAS-attached to s single host. Gpfsperf reported 3,2 Gbyte/s for writes.
and 250-300 Mbyte/s on sequential reads!! Random reads were on the order
of 2 Gbyte/s.
After a bit head scratching snd fumbling around I found out that reducing
maxMBpS from 10000 to 100 fixed the problem! Digging further I found that
reducing prefetchThreads from default=72 to 32 also fixed it, while
leaving maxMBpS at 10000. Can now also read at 3,2 GByte/s.
Could something like this be the problem on your box as well?
-jf
fre. 17. feb. 2017 kl. 18.13 skrev Aaron Knister <aaron.s.knister at nasa.gov
>:
Well, I'm somewhat scrounging for hardware. This is in our test
environment :) And yep, it's got the 2U gpu-tray in it although even
without the riser it has 2 PCIe slots onboard (excluding the on-board
dual-port mezz card) so I think it would make a fine NSD server even
without the riser.
-Aaron
On 2/17/17 11:43 AM, Simon Thompson (Research Computing - IT Services)
wrote:
> Maybe its related to interrupt handlers somehow? You drive the load up
on one socket, you push all the interrupt handling to the other socket
where the fabric card is attached?
>
> Dunno ... (Though I am intrigued you use idataplex nodes as NSD servers,
I assume its some 2U gpu-tray riser one or something !)
>
> Simon
> ________________________________________
> From: gpfsug-discuss-bounces at spectrumscale.org[
gpfsug-discuss-bounces at spectrumscale.org] on behalf of Aaron Knister [
aaron.s.knister at nasa.gov]
> Sent: 17 February 2017 15:52
> To: gpfsug main discussion list
> Subject: [gpfsug-discuss] bizarre performance behavior
>
> This is a good one. I've got an NSD server with 4x 16GB fibre
> connections coming in and 1x FDR10 and 1x QDR connection going out to
> the clients. I was having a really hard time getting anything resembling
> sensible performance out of it (4-5Gb/s writes but maybe 1.2Gb/s for
> reads). The back-end is a DDN SFA12K and I *know* it can do better than
> that.
>
> I don't remember quite how I figured this out but simply by running
> "openssl speed -multi 16" on the nsd server to drive up the load I saw
> an almost 4x performance jump which is pretty much goes against every
> sysadmin fiber in me (i.e. "drive up the cpu load with unrelated crap to
> quadruple your i/o performance").
>
> This feels like some type of C-states frequency scaling shenanigans that
> I haven't quite ironed down yet. I booted the box with the following
> kernel parameters "intel_idle.max_cstate=0 processor.max_cstate=0" which
> didn't seem to make much of a difference. I also tried setting the
> frequency governer to userspace and setting the minimum frequency to
> 2.6ghz (it's a 2.6ghz cpu). None of that really matters-- I still have
> to run something to drive up the CPU load and then performance improves.
>
> I'm wondering if this could be an issue with the C1E state? I'm curious
> if anyone has seen anything like this. The node is a dx360 M4
> (Sandybridge) with 16 2.6GHz cores and 32GB of RAM.
>
> -Aaron
>
> --
> Aaron Knister
> NASA Center for Climate Simulation (Code 606.2)
> Goddard Space Flight Center
> (301) 286-2776
> _______________________________________________
> gpfsug-discuss mailing list
> gpfsug-discuss at spectrumscale.org
> http://gpfsug.org/mailman/listinfo/gpfsug-discuss
> _______________________________________________
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>
--
Aaron Knister
NASA Center for Climate Simulation (Code 606.2)
Goddard Space Flight Center
(301) 286-2776
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