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Unexpected benefit with Ryzen – reducing power for build server

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Re: Unexpected benefit with Ryzen – reducing power for build server

#11

Post by gizmo686 »

lykr0n wrote: post #8
Jonnax wrote: post #4

180w to 85w is pretty impressive. I didn't know that compilation was memory speed limited. Are there any good benchmarks on it? Anyone have any examples of getting faster memory boosting build speed? Over the last few years I'd settled into thinking that high speed ram barely did anything. I guess I was wrong!

ryzen loves memory speed, more so than Intel. phoronix has benchmarks that you're looking for. https://www.phoronix.com/scan.php?page=article&item=ryzen-dd...

More specifically, the interprocessor interconnect (infinity fabric) system ryzen uses is tied to the RAM clock. Ryzen clumps there processosor in groups of 4, and uses infinity fabric as an interconnect between those; so I am not sure you will an effect larger then Intel on a quadcore ryzen.

https://www.techpowerup.com/231585/amd-ryzen-infinity-fabric...

Re: Unexpected benefit with Ryzen – reducing power for build server

#12

Post by Nux »

ddorian43 wrote: post #9
Nux wrote: post #6

Earlier quoted context omitted.

"128 GB DDR4 ECC RAM" .. sounds pretty ECC to me.

I was talkin about Ryzen 8core more actually. Those have low clock speed. And are called EPYC.

Got it. For what it's worth I think EPYC is based on the same "Zen" arch as Ryzen.

Re: Unexpected benefit with Ryzen – reducing power for build server

#13

Post by _wmd »

Jonnax wrote: post #4

180w to 85w is pretty impressive. I didn't know that compilation was memory speed limited. Are there any good benchmarks on it? Anyone have any examples of getting faster memory boosting build speed? Over the last few years I'd settled into thinking that high speed ram barely did anything. I guess I was wrong!

Anything involving larger-than-cache sized graph walks will usually be memory limited, be it compilation or iterating an XML document

Re: Unexpected benefit with Ryzen – reducing power for build server

#14

Post by BeeOnRope »

magila wrote: post #7

Calling this "Unexpected" seems like a bit of a stretch. In particular this part: > Of course, in the server space, we've known for a long time that maximum efficiency occurs with a high number of cores running at lower frequencies, and that efficiency trumps performance on machines with high core counts. But I never considered that the consumer Ryzen CPUs could also benefit from the same thing until now. makes no se…

Well I suppose the part that might not apply to desktop parts is "efficiency trumps performance". Many desktop uses don't care about efficiency, but care about performance.

For servers, the purchasing decisions are probably much more quantitative, and if you are buying a high core count machine it probably means you have a parallelizable workload, so no efficiency comes into play since you have a lot of choice on the frequency/core-count spectrum, versus power, money, space, etc.

Re: Unexpected benefit with Ryzen – reducing power for build server

#15

Post by BeeOnRope »

ceratopisan wrote: post #10
magila wrote: post #7

Calling this "Unexpected" seems like a bit of a stretch. In particular this part: > Of course, in the server space, we've known for a long time that maximum efficiency occurs with a high number of cores running at lower frequencies, and that efficiency trumps performance on machines with high core counts. But I never considered that the consumer Ryzen CPUs could also benefit from the same thing until now. makes no se…

You are confusing principle with implementation. Reducing clock speed reduces power usage and you can compensate with more cores is indeed a truth. However, finding that option in consumer hardware has been relatively difficult. That is the surprise indicated.

Note that the author is not claiming that he compensated with more cores. He is claiming that the performance is roughly the same, at the same core count (8), regardless of frequency.

Re: Unexpected benefit with Ryzen – reducing power for build server

#17

Post by wolf550e »

Not every workload is memory bandwidth bound like his "make -j16" compile. Some workloads need memory latency or fast inter-core (and inter-socket) operations (e.g. RDBMS OLTP), some need CPU throughput (e.g. HPC), some need best possible single thread CPU performance (e.g. some gaming).

As he wrote, CPUs are most efficient (compute per Watt) at a specific frequency, and if his CPU mostly waits for RAM, this can be done at low power.

It's probably possible to create x86-64 CPUs with narrower backends (fewer execution units) with microcode-emulated 128 and 256 bit registers/operations (and maybe even emulated FPU) and get a cheaper and faster build server, if it was economical to fab such narrow-use-case chips (those would be good for redis/memcached too I imagine).

Re: Unexpected benefit with Ryzen – reducing power for build server

#18

Post by magila »

ceratopisan wrote: post #10
magila wrote: post #7

Calling this "Unexpected" seems like a bit of a stretch. In particular this part: > Of course, in the server space, we've known for a long time that maximum efficiency occurs with a high number of cores running at lower frequencies, and that efficiency trumps performance on machines with high core counts. But I never considered that the consumer Ryzen CPUs could also benefit from the same thing until now. makes no se…

You are confusing principle with implementation. Reducing clock speed reduces power usage and you can compensate with more cores is indeed a truth. However, finding that option in consumer hardware has been relatively difficult. That is the surprise indicated.

Ryzen is known to be memory constrained even with much faster memory than he used. It is completely predicable that he found his CPU to be severely starved for memory bandwidth thus enabling him to reduce operating frequency without penalty.

This is like putting an LS engine in an otherwise stock Miata and acting surprised that you can run the engine at lower RPM and still put in good lap times.

Re: Unexpected benefit with Ryzen – reducing power for build server

#19

Post by ddorian43 »

BeeOnRope wrote: post #16
ddorian43 wrote: post #2

Any server-hosting with Ryzen + ecc-ram ?

Packet.net offers it: https://www.packet.net/bare-metal/servers/c2-medium-epyc/

Please see other comments. It's EPYC and not RYZEN. 2.0 Ghz base clock speed is not nice for single-thread.
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