[gpfsug-discuss] bizarre performance behavior

Jan-Frode Myklebust janfrode at tanso.net
Fri Feb 17 18:29:46 GMT 2017


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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> > http://gpfsug.org/mailman/listinfo/gpfsug-discuss
> >
>
> --
> 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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