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Old 2012-12-29, 16:06   #1
pepi37
 
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Default AVX on AMD processors.

Can someone tell me when ( or will be ever) made LLR that can use AVX built in AMD processors?
Currently LLR can use AVX on Intel processors, but no use on AMD.
Thanks for answer
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Old 2012-12-29, 16:34   #2
Prime95
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Quote:
Originally Posted by pepi37 View Post
Can someone tell me when ( or will be ever) made LLR that can use AVX built in AMD processors?
Currently LLR can use AVX on Intel processors, but no use on AMD.
Thanks for answer
AVX on AMD processors is slower than SSE2 on AMD processors.
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Old 2013-01-03, 19:13   #3
ewmayer
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AVX on AMD processors is slower than SSE2 on AMD processors.
You'd think they might have done a few of those obscure things called "benchmarks" before selling those "AVX supporting" CPUs, but that's the sort of bizarre things companies which wrong-headedly focus on "staying in business" do.

To think that it was only a few years ago - in the wake of Athlon/Opteron debuting - that AMD actually, briefly pulled even with Intel in terms of market share. Been all (self-inflictedly) downhill for them since then.
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Old 2013-01-08, 14:18   #4
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Originally Posted by ewmayer View Post
To think that it was only a few years ago - in the wake of Athlon/Opteron debuting - that AMD actually, briefly pulled even with Intel in terms of market share. Been all (self-inflictedly) downhill for them since then.
Don't want to start a flame war, but when you are fighting against a company that has doubtful business practices, it's quite difficult to succeed, especially when the said company also has very talented engineers.
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Old 2013-01-08, 14:20   #5
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wait, which is the most important? very talented engineers or shady practice?
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Old 2013-01-08, 14:25   #6
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wait, which is the most important? very talented engineers or shady practice?
The most important is talented engineers that can produce things that can be sold in a free market where your competitor isn't giving money and/or heavily reduces its prices to prevent you from competing. AMD also has (had?) very talented engineers you know :)
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Old 2013-01-08, 20:20   #7
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If you follow this link you can clearly see that AVX , properly enabled gives speed nearly same as Intel I7

http://www.lostcircuits.com/mambo//index.php?option=com_content&task=view&id=102&Itemid=42&limit=1&limitstart=13
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Old 2013-01-08, 20:50   #8
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Originally Posted by pepi37 View Post
If you follow this link you can clearly see that AVX , properly enabled gives speed nearly same as Intel I7

http://www.lostcircuits.com/mambo//index.php?option=com_content&task=view&id=102&Itemid=42&limit=1&limitstart=13
One of the benchmarks shows severe performance hits (64%), others show slowdowns when AVX is used. Have you actually read the article?

Last fiddled with by Ralf Recker on 2013-01-08 at 21:19 Reason: Wording
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Old 2013-01-08, 21:25   #9
Prime95
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If you follow this link you can clearly see that AVX , properly enabled gives speed nearly same as Intel I7
Don't believe everything you read.

The only advantage to 256-bit AVX in Bulldozer is a reduction in instruction decode bandwidth. This is rarely a problem doing floating point operations.

The downsides are numerous:

1) A 256-bit AVX store is a micro-coded instruction - which can cause bubbles in the instruction decoder. This critical instruction is 3 or 4 uops vs. SSE2 requiring 2 128-bit stores which are easily decoded and take just 2 uops.

2) Swizzling data for a 256-bit register takes twice as much work as swizzling data for a 128-bit register. Bulldozer is horribly slow at swizzling.

3) While not an AVX problem, IMO the load store unit is miserable. I have simple macros that should take 26 clocks. In fact they do if you don't store any results. Add in the storing of data and the macro balloons to 39 clocks. AMD literature indicates the chip should be able to support the load/store throughput of the macro. Phenom also was pretty dreadful in this regard.

I can use AVX to make prime95 on Bulldozer a little faster. I can take the SSE2 code and use the AVX fused-multiply-add instruction to make some small improvements (if the load-store unit will let me).

This will not let Bulldozer approach Sandy/Ivy Bridge speed. Yes, they have the same *theoretical* float throughput. But, Intel can get much closer to the theoretical because Intel can do 1 256-bit add and mul per clock. AMD can only do a *fused* mul/add per clock. Not all muls and adds can be fused. Intel does not have AMD's strange load-store penalty. My macros on Intel CPUs typically run about 10% slower than best case.

More bad news for AMD. Haswell will double Intel FPU theoretical throughput.
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Old 2013-01-08, 22:31   #10
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Quote:
Originally Posted by ldesnogu View Post
The most important is talented engineers that can produce things that can be sold in a free market where your competitor isn't giving money and/or heavily reduces its prices to prevent you from competing. AMD also has (had?) very talented engineers you know :)
In the classic effective-monopoly paradigm, shady business practices allow the market-share dominant player to put inferior products (for their price) into the market without suffering the market share loss they would in a genuinely competitive space.

In this case you admit AMD has talented engineers, implying their "evil" competitor's shady business practices are not hindering them in the product-development area. And yet here it is AMD which is clearly and consistently bringing inferior products to the marketplace, and Intel which is meeting and even exceeding the hopes of us "throughput addicts", which is what any high-performance code developer worth his salt must by necessity be. That is why I don't buy the standard "our competitor is an evil monopolist" argument. The last time AMD came out with a genuinely competitive product, they very rapidly gained market share and pulled even with Intel, until they again stumbled on the execution front.

Note that I have no personal stake in the ever-ongoing chip war except in the "whose product do I want to spend my time testing/tuning code on?" sense. Don't own shares in either company, not looking to make any speculative stock-market plays here. But I am planning to by an AVX2-capable MoBo as soon as they hit market.
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Old 2013-01-09, 09:14   #11
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Originally Posted by Prime95 View Post
Haswell will double Intel FPU theoretical throughput.
Yarrrrr!

Most probably I won't invest in a new system soon (in the next 2-3-5 years, I have already too much hardware, except in the case something bad happens with my current farm - god forbid that).

But this announcement feels so good to read!

Last fiddled with by LaurV on 2013-01-09 at 09:15
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