RAM Upgrade Necessary?

Kopzr · May 22, 2018, 20:56

Hello,

I am competing on SAEs aerodesign competition and desperately need to accelerate my CFDs.

Earlier this year I bought a new computer aiming to learn and perform CFD analisys on our aeroplane, it has the following specs:

CPU: Ryzen 7 1700x
GPU: RX570
RAM: 8GB Ram branded as dell
HDD: 1TB 7200rpm

I am running simulations on fluent with ~1mil elements @ ansys 16, and it is taking a full-day to perform 2k iterations at double precision, using all 8 cores. Since it takes 4-8k iterations for the simulation to converge it is taking a LOT of time.

Comparatively, a computer in my university, equipped with an i7-2600 and 16GB RAM, performs about 8k iterations in a single day.

Is this performance gap being caused only by RAM, or is there something I am missing here?

Thanks,

pibil1 · May 23, 2018, 00:02

It looks like you are using 1 8GB stick and they are usind two 8GB ram sticks, obtaining more memory bandwidth. They might be using ddr3 3200 Mhz too. Can't you check your university pc please?

flotus1 · May 23, 2018, 03:50

With the older PC being effectively 4x faster, there must be a lot going on.
Checklist in no particular order:

Use 2 identical DIMMs for your Ryzen PC. Preferably, either very fast single-rank modules ~DDR4-3200 or moderately fast dual-rank modules ~DDR4-2800. Assuming the motherboard has at least a B350 chipset. But even adding another DIMM similar to the one you already have would help. In that case, make sure the amount of ranks is identical.
make sure your CPU is running at maximum frequency under full load and not hindered e.g. by some energy saving option in your OS
disable SMT in the bios
check if your simulation might run faster using less than 8 cores
Potential I/O bottleneck thanks to the slow hard drive? Are you writing lots of results during the simulation, how is HDD usage during simulation?
are both PCs running the same OS?

LuckyTran · May 23, 2018, 08:39

Have you done the obvious checks like checking the cpu usage? I.e. task manager in Windows? Make sure the running cpu's are at 100% and RAM is not overloaded. Your simulation probably eats <4-6GB of RAM, but if your OS uses up 3GB then you're already out of memory.

May 22, 2018, 20:56	RAM Upgrade Necessary?	#1
Kopzr New Member Renan Join Date: Mar 2016 Posts: 4 Rep Power: 10	Hello, I am competing on SAEs aerodesign competition and desperately need to accelerate my CFDs. Earlier this year I bought a new computer aiming to learn and perform CFD analisys on our aeroplane, it has the following specs: CPU: Ryzen 7 1700x GPU: RX570 RAM: 8GB Ram branded as dell HDD: 1TB 7200rpm I am running simulations on fluent with ~1mil elements @ ansys 16, and it is taking a full-day to perform 2k iterations at double precision, using all 8 cores. Since it takes 4-8k iterations for the simulation to converge it is taking a LOT of time. Comparatively, a computer in my university, equipped with an i7-2600 and 16GB RAM, performs about 8k iterations in a single day. Is this performance gap being caused only by RAM, or is there something I am missing here? Thanks,

May 23, 2018, 03:50		#3
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,400 Rep Power: 47	With the older PC being effectively 4x faster, there must be a lot going on. Checklist in no particular order: Use 2 identical DIMMs for your Ryzen PC. Preferably, either very fast single-rank modules ~DDR4-3200 or moderately fast dual-rank modules ~DDR4-2800. Assuming the motherboard has at least a B350 chipset. But even adding another DIMM similar to the one you already have would help. In that case, make sure the amount of ranks is identical. make sure your CPU is running at maximum frequency under full load and not hindered e.g. by some energy saving option in your OS disable SMT in the bios check if your simulation might run faster using less than 8 cores Potential I/O bottleneck thanks to the slow hard drive? Are you writing lots of results during the simulation, how is HDD usage during simulation? are both PCs running the same OS?

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May 23, 2018, 00:02		#2
pibil1 New Member Join Date: Aug 2017 Posts: 28 Rep Power: 8	It looks like you are using 1 8GB stick and they are usind two 8GB ram sticks, obtaining more memory bandwidth. They might be using ddr3 3200 Mhz too. Can't you check your university pc please?

May 23, 2018, 08:39		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,677 Rep Power: 66	Have you done the obvious checks like checking the cpu usage? I.e. task manager in Windows? Make sure the running cpu's are at 100% and RAM is not overloaded. Your simulation probably eats <4-6GB of RAM, but if your OS uses up 3GB then you're already out of memory.