[gpfsug-discuss] bizarre performance behavior

Fri Apr 21 14:10:49 BST 2017

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><mailto: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 <<mailto:aaron.s.knister at nasa.gov>aaron.s.knister at nasa.gov<mailto: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<mailto:gpfsug-discuss-bounces at spectrumscale.org> [<mailto:gpfsug-discuss-bounces at spectrumscale.org>gpfsug-discuss-bounces at spectrumscale.org<mailto:gpfsug-discuss-bounces at spectrumscale.org>] on behalf of Aaron Knister [<mailto:aaron.s.knister at nasa.gov>aaron.s.knister at nasa.gov<mailto: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
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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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