Quite a few Polaris GPUs are limited by ROP/bandwidth compared to older GCN cards.

[tamz_msc]

First the videos, Dota 2 and Dirt Rally.

Now the specs:

R7 370 - 1024:64:32 (SP:TMU:ROP), 985 MHz core, 5600 MT/s memory, 256 bit, 179.2 GB/s.
RX 560 - 1024:64:16 (SP:TMU:ROP), 1300 MHz core, 7000 MT/s memory, 128 bit, 112 GB/s.

R7 250 - 512:32:16 (SP:TMU:ROP), 925 MHz core, 4500 MT/s memory, 128 bit, 72 GB/s.
RX 550 - 512:32:16 (SP:TMU:ROP), 1206 MHz core, 7000 MT/s memory, 128 bit, 112GB/s.

As the results clearly indicate, the RX 560 isn't much faster than the R7 370, while the RX 550 leaves the R7 250 behind by a country mile. Since the hypothetical equivalents to Hawaii don't exist, there is no direct comparison. But it's clear from these results that Vega isn't the only architecture that is bottlenecked by ROP and bandwidth.

 

[SPBHM]

the difference in memory bandwidth makes this comparison problematic,

also r7 250 = 384SPs, 8 ROPs, 24 TMUs

 

[tamz_msc]

There are a lot of variants of the R7 250 GPU. The one in the video is the 512 sp one.

 

[IRobot23]

Yeah, RX 580 has only 32ROPs while competing against R9 390/X. Also +50% less bandwidth.
But both have similar front end. Same goes for RX 560 and R7 370.

This is why VEGA is fail. Similar performance of front end as RX 580.

When you see VEGA doing good, you gonna see also R9 Fury X, R9 280X and so on unless RAM amount is a problem.

 

[SPBHM]

There are a lot of variants of the R7 250 GPU. The one in the video is the 512 sp one.

well what a mess, originally the r7 250 used the Oland GPU with 384SPs, after a while they released the 250x which was a 7770 rebrand, and then I saw some 7750 rebrands as 250E I think...

if the specs are correct this "250" you are comparing is a 7750 with higher clocks

in any case, I do think that the memory bandwidth on these cards make the comparison difficult;

Computerbase tested here Dirt Rally with a 280x (Tahiti), 380x (Tonga) and 470 (all 2048SPs, 32 ROPs) at the same clock with similar memory bandwidth;
on Dirt Rally Polaris was only 6% faster and the other 2 equal
https://www.computerbase.de/2016-08...-performance/2/#diagramm-dirt-rally-1920-1080

so I think it's one game bellow average in terms of showing the Polaris improvements;
and with the 370 vs 560 you have a big advantage for the 370 in terms of memory bandwidth, and the "250" with a big disadvantage, so I don't find it very conclusive....

 

[tamz_msc]

I've never seen memory bandwidth alone accounting for the kind of differences that you are seeing between the RX550 and the R7 250. One indication of this being the case is that the Vega 8 iGPU memory scaling tapers out long before you reach the kind of bandwidth that these cards have.

 

[SPBHM]

performance to avoid the video:

relative to the 550 (Polaris) we have the 250 (7750 OC; GCN1.0) as
76% of the GPU clock
64% of the memory bandwidth
70% of the performance in Dirt Rally


with the 370 (7850 OC; GCN 1.0) relative to the 560 (Polaris) we have the same number of units apart from
200% ROPs
75% of the GPU clock
160% memory bandwidth
91% of the performance in Dirt Rally

but we have Vega 8,

according to TPU Vega 8 specs are 8 ROPs, 32 TMUs, 512SPs at 1100MHz, memory speed on the test was 3200 128bit, so "51.2"GB/s

compared to the 550 we get, same number of units apart from 50% ROPs
91% of the GPU clock
46% of the memory bandwidth
72% of the performance in Dirt Rally

I'm not using the Vega 8 OC results, because he also overclocks the CPU clock for that one, while others run with the CPU at stock, still the OC is from 1100 to 1600MHz, while apparently keeping the memory stuck at 3200.

do you think this is conclusive as the ROPs being the main bottleneck?
I'm not so sure.

it's very difficult to quantify the architecture efficiency gains just looking at these numbers, earlier I quoted a 6% from Tahiti/Tonga to Polaris, but even that, it's a very old result with older drivers....

also, it would be necessary to investigate if the stock 2200G is not bottlenecking the 560 since it's running at a high framerate (98)

 

[tamz_msc]

Nah I'm pretty sure there is no CPU bottleneck, even with OC. You need a GTX 1070 to see the CPU being a factor in frame rates, according to Steve @ Hardware Unboxed. I'm not comparing against the Vega 8 though, just saying that the memory bandwidth scaling shows that Vega 8 cares more about memory bandwidth(up to a point) since it has already pretty low bandwidth to begin with. Given what we know about GPU overclocking, these low end GPUs are more limited by core clock than memory clock, so I don't think that the memory bandwidth difference is that important a factor in the RX 550 vs R7 250 comparison.