Considering a new GPU soon. How's the 7700 series on Linux?

[Kano]

@bridgman

Do you really need to buy gfx cards? What does amd do with all the test samples?

[curaga]

@Bridgman

In the last optimized test a month ago (http://www.phoronix.com/scan.php?pag...ompete12&num=1 ), the low-end card (6450) was 1/2 to 1/6 of the blob.

That is a higher difference than with more powerful cards, which goes against what you've said earlier - that the high-end cards would have a larger difference to the blob.

What's your opinion on this?

[bridgman]

In the last optimized test a month ago (http://www.phoronix.com/scan.php?pag...ompete12&num=1 ), the low-end card (6450) was 1/2 to 1/6 of the blob. That is a higher difference than with more powerful cards, which goes against what you've said earlier - that the high-end cards would have a larger difference to the blob. What's your opinion on this?

I have normally recommended mid-range cards rather than low end. The simple explanation for that is "open source drivers are currently slower so get a faster card", but there's actually more to it (as you noticed). Here we go...

On the high end it's hard to make full use of the hardware with open source drivers with the current level of driver optimization for *CPU* usage, ie there's a good chance the drivers will bottleneck on CPU before they fully utilize the GPU on most workloads. Note that as shader workloads become more complex high end cards become more attractive even without further driver optimizations.

On the low end the issue is that the die area allocation on low end part is usually optimized for different workloads than on the midrange and high end parts (all vendors, not just us). Specifically, the ratio between shader throughput (ALUs) and pixel/texel throughput (texture units / ROPs) changes, with low end parts having relatively less shader power compared to pixel-pushing ability. This makes sense if you think about it -- you don't expect low end parts to deliver the same gaming experience but you still expect basic 2D operations to happen snappity-quick. The differences are less drastic on newer discrete GPU families because integrated graphics have displaced the very low end discrete GPU market, but even on the HD 6xxx family there's maybe a 10:1 difference in shader throughput vs only 4:1 difference in pixel throughput.

This isn't particularly meaningful on its own, but if you combine the above point with the fact that shader compiler optimization is usually one of the last things to happen in an open source driver, you get the result that shader-intensive workloads on low end hardware with open source drivers are likely to bottleneck on the shader core first, while running the same workload on midrange hardware would be more likely to "bottleneck on everything at the same time" because the balance between hardware resources is different.

If you look at results on specific benchmarks, you'll see the relative performance on low-end hardware is higher on programs with simpler shaders. It's all about the *first* bottleneck you hit - low end cards tend to hit shader limits first, high end cards tend to hit CPU limits first. Make sense ?

@bridgman

Do you really need to buy gfx cards? What does amd do with all the test samples?

The early engineering samples can be flakey and not something I would want in my home system. Since we have a unified driver, the later samples get kept around for testing new driver changes on older hardware. If I just wanted free hardware I could probably wait around until we EOL'ed HW generations and see what I could scrounge, but I didn't want to wait that long particularly since the open source drivers have caught up with newer hardware.

In my point of view business is all about economy and if the optimization of the last bits burn all the money "Driver optimization is definitely a case of *seriously* diminishing returns as you go further up the curve." then its not the smart way to do business. If it were my company I would make a study about worth it or not. I'm sure AMD don't even think in this rational logical way. My advice to AMD is: Cut costs to increase profit by act rational/logical by drop closed source drivers.

We have this discussion every year or so. Problem is that a lot of PC industry buying decisions are still reliant on feature checklists and benchmark numbers. Having all the right answers to the questions isn't enough to get you the order, but missing a feature or being a few percent down on performance is enough to disqualify you. There's a theorem somewhere that says it's dangerous to be more rational and logical than your market.

This is part of the bigger challenge we all face, specifically that supply chains win by simplifying and reducing choices (eg "what the heck, why bother with Linux ?) even though the people who actually buy and use the hardware want more choice and more support for their specific needs. The result is arguably a "race to the bottom", eg where every bookstore sells the same top-30 best sellers and nothing else because that works best for *them* even if it sucks for the customer.

If you want to avoid that race to the bottom you need to play both short term and long term games at the same time, which may seem wasteful but may also be unavoidable for a while.

[maldorordiscord]

We have this discussion every year or so. Problem is that a lot of PC industry buying decisions are still reliant on feature checklists and benchmark numbers. Having all the right answers to the questions isn't enough to get you the order, but missing a feature or being a few percent down on performance is enough to disqualify you. There's a theorem somewhere that says it's dangerous to be more rational and logical than your market.

LOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOL
But best explanation you have ever given to me!
Damn these stupid people damn I'm to rational and to logical for this kind of world damn!
Really just: damn...

Mankind just lost all hope.

Anyway if I buy a hd7970 can I get the 100€ "catalyst" closed-source-tax back if I promise I will use the open-source driver?
Can we please get a Catalyst incompatible firmware to make sure we don't need to pay the catalyst-closed-source-tax ?
AMD really should pay 100€(for a hd7970) compensation to opensource driver users!
In fact if I buy a AMD card I pay the (29/30)catalyst-closed-source-tax and I only get (1/30) open-source improvement for my money :-( this is so sad.

This catalyst-closed-source-tax is just unfair!

[curaga]

This isn't particularly meaningful on its own, but if you combine the above point with the fact that shader compiler optimization is usually one of the last things to happen in an open source driver, you get the result that shader-intensive workloads on low end hardware with open source drivers are likely to bottleneck on the shader core first, while running the same workload on midrange hardware would be more likely to "bottleneck on everything at the same time" because the balance between hardware resources is different.

If you look at results on specific benchmarks, you'll see the relative performance on low-end hardware is higher on programs with simpler shaders. It's all about the *first* bottleneck you hit - low end cards tend to hit shader limits first, high end cards tend to hit CPU limits first. Make sense ?

Good explanation, thanks. I'd like your opinion then on the old OpenArena result, a shaderless test.
Almost all cards were nearly exactly 50% of the blob, including the low-end card.

I doubt the Q3-specific optimizations apply to OA, as I recall someone testing OA with the binary name changed to that of Q3 and getting more speed under the blob.

Since on these generations the fixed function is done via emulation shaders, does that mean that these emulation shaders are crappy? Or that the hw-specific shader compiler would be able to make better use of them, and that they are good at the TGSI level?

[bridgman]

This catalyst-closed-source-tax is just unfair!

It's like a buffet... if you fill up on ham we don't charge you for the roast beef

Good explanation, thanks. I'd like your opinion then on the old OpenArena result, a shaderless test.
Almost all cards were nearly exactly 50% of the blob, including the low-end card.

I doubt the Q3-specific optimizations apply to OA, as I recall someone testing OA with the binary name changed to that of Q3 and getting more speed under the blob.

Since on these generations the fixed function is done via emulation shaders, does that mean that these emulation shaders are crappy? Or that the hw-specific shader compiler would be able to make better use of them, and that they are good at the TGSI level?

Good question. My first thought would be that the fixed function apps are likely to be CPU limited but don't know if anyone has looked at them recently. Once the frame rates get over a certain point it's better to spend time on something that runs more slowly...

IIRC the ff emulation shaders are pretty simple so I wouldn't expect to be shader limited even on the low end cards. Unfortunately all of the performance numbers are ugly 1/(1/A + 1/B +... ) kinds of things so you don't get nice clean breakpoints from shader or CPU or other limiting.

[curaga]

Unfortunately all of the performance numbers are ugly 1/(1/A + 1/B +... ) kinds of things so you don't get nice clean breakpoints from shader or CPU or other limiting.

You'd have those numbers if the performance counters were available

[bridgman]

You'd have *more* numbers but still not enough to make it easy. Performance optimization still follows the scientific method :

10 look through reams of information, pull theory out of <body part>
20 implement proof-of-concept, see if it makes target app go faster
30 excited by performance improvement on target app, test a bunch of other apps
40 depressed by performance reduction on other apps, GOTO 10

And yes, the scientific method pre-dates structured programming

[Veto]

@ bridgman: Thank you for a long and enlightening post. I find it highly reassuring, that you have the time and willingness to answer questions in these fora - even though the questions may be of lesser quality than your answers.

Anyway if I buy a hd7970 can I get the 100€ "catalyst" closed-source-tax back if I promise I will use the open-source driver?
Can we please get a Catalyst incompatible firmware to make sure we don't need to pay the catalyst-closed-source-tax ?

Try to think yourself about the ramifications of your suggestions for a moment... We do not need even more division and incompatibility. (Like a "Linux Only" graphics card would be a huge sustainable success - dooooh! )

[maldorordiscord]

It's like a buffet... if you fill up on ham we don't charge you for the roast beef

Sure but its not a buffet!
For a rational human the conclusion is: don't buy AMD hardware if you are a open-source driver user because you will subsidize the closed source driver because for every euro the closed source makes a higher percentage because the prices are determined by the closed source driver team and you get less features if you use the open-source driver and there is no compensation to open-source users.

Market economy based opensource driver users hurt them self by buying AMD hardware.

I needed long time to understand this lever.

Now the question is what to buy to max the pressure against this evil antisocial "Lever" ?

ARM based systems without windows support and without closed source drivers?
Intel systems with OEM Linux on it to make sure open-source is the case?
Stop playing games and use 3D features at all?
Buying server hardware clusters and use software-openGL-cpu rendering?

This evil antisocial "Lever" must definitely be stopped.