[gpfsug-discuss] bizarre performance behavior

Fri Apr 21 10:50:55 BST 2017

Hi,

prefetching was already disabled at our storage backend, but a good 
thing to recheck :)

thanks!

On 20/04/17 17:07, Uwe Falke wrote:
> Hi Kennmeth,
>
> is prefetching off or on  at your storage backend?
> Raw sequential is very different from GPFS sequential at the storage
> device !
> GPFS does its own prefetching, the storage would never know what sectors
> sequential read at GPFS level maps to at storage level!
>
>   
> Mit freundlichen Grüßen / Kind regards
>
>   
> Dr. Uwe Falke
>   
> IT Specialist
> High Performance Computing Services / Integrated Technology Services /
> Data Center Services
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>
> From:   Kenneth Waegeman <kenneth.waegeman at ugent.be>
> To:     gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
> Date:   04/20/2017 04:53 PM
> Subject:        Re: [gpfsug-discuss] bizarre performance behavior
> Sent by:        gpfsug-discuss-bounces at spectrumscale.org
>
>
>
> 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
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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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