AMD 300 Series reviews ...

[silent_guy]

That 384-bit bus on Tonga was just a dumb mistake.... (http://www.pcper.com/news/Graphics-...a-384-bit-Memory-Bus-Not-Enabled-Any-Products)

The reason? The company never found the right price/performance combination.

One wonders how many millions were left on the table right there...

Are the L2 caches tied to the memory controller?

 

[3dilettante]

That 384-bit bus on Tonga was just a dumb mistake.... (http://www.pcper.com/news/Graphics-...a-384-bit-Memory-Bus-Not-Enabled-Any-Products)

Koduri actually discussing the inactive interface that must have been a condition of Scott Wasson's employment, since that was a pet theory of his at Techreport even prior to the die shot.

I imagine that AMD had envisioned a market slot for the fully-enabled Tonga. Was there a plan to fully phase out Tahiti and bracket its position with Tonga and Hawaii? Did the whole pricing stack get squashed, and just how bad was the glut due to AMD's response to the cryptomining bubble?

Are the L2 caches tied to the memory controller?

There is an L2 slice per channel, so 1/3 of the L2 would have been inactive as well.

 

[Dave Baumann]

IIRC Tonga is a little different in this regard.

 

[3dilettante]

The most prominent recipient of top-tier Tonga devices was Apple, whose influence for justifying Tonga's odd placement was another pet theory at TR. Apple could have paid for the extra bus to be used if it wanted to, maybe?

 

[silent_guy]

Koduri actually discussing the inactive interface that must have been a condition of Scott Wasson's employment, since that was a pet theory of his at Techreport even prior to the die shot.

Of course!

There is an L2 slice per channel, so 1/3 of the L2 would have been inactive as well.

It's not very clear on that PC watch diagram. If they can use the full L2 even with a 256-bit bus, the silicon waste would be a bit more reasonable. Still puzzling though.

 

[3dilettante]

It's not very clear on that PC watch diagram. If they can use the full L2 even with a 256-bit bus, the silicon waste would be a bit more reasonable. Still puzzling though.

GCN's L2 statically links a slice to a channel. It's how GCN's cache remains "coherent" at the L2 level. As a physical location can only be cached in a fixed slice, it is trivially coherent.

 

[DuckThor Evil]

That 384-bit bus on Tonga was just a dumb mistake.... (http://www.pcper.com/news/Graphics-...a-384-bit-Memory-Bus-Not-Enabled-Any-Products)

One wonders how many millions were left on the table right there...

It's a little bit tricky because 384-bit bus would in practice mean 3GB or 6GB of memory and both of those pose some issues. 3GB is a bit low for this 380X and 6GB an overkill and factoring in that Fury only has 4GB it would look a little odd. It's a pity it never showed up, but perhaps we didn't really lose much by missing it...

 

[3dilettante]

IIRC Tonga is a little different in this regard.

My apologies since I've gone afar on the L2 topic already, but I read this and initially interpreted it as referencing something else. On second thought, was this in regard to Tonga's L2? I've seen various reviews that gave it a size matching the bus width, but perhaps they were assuming.

 

[ImSpartacus]

It's a little bit tricky because 384-bit bus would in practice mean 3GB or 6GB of memory and both of those pose some issues. 3GB is a bit low for this 380X and 6GB an overkill and factoring in that Fury only has 4GB it would look a little odd. It's a pity it never showed up, but perhaps we didn't really lose much by missing it...

I think it's not completely unreasonable to see a fully enabled 6GB Tonga variant as part of the 400 series.

In 2015's lineup, AMD has already demonstrated two things with respect to VRAM that would enable a 6GB Tonga-based part:

• If they can't convincingly beat the competition, AMD is more than willing to play the VRAM-inflation game to at least gain that marketing edge. Grenada's overly generous 8GB of VRAM was probably unnecessary in the face of the 4GB 970 & 980, but AMD did it anyway. Future cards near the all-important $200 mark will almost certainly sport at least 4GB of VRAM (They are already a regular appearance at that price point, especially in the 960).
  
• AMD can tolerate a "VRAM-backwards" lineup to the chagrin of the unfortunately limited 4GB Fiji parts. AMD had no problem selling a $330 8GB 390 in the same lineup as their $650 4GB Fury X. Obviously, I'm sure that they would've preferred to do things differently, but they did it and they will probably have continue doing it as long as they keep selling Fiji-based parts at remotely profitable prices.

So I don't think it would be all that surprising to see a ~$200 6GB Tonga-based part in mid-2016 when the 400s start trickling out.

Furthermore, it's not inconceivable that an 8GB Hawaii grandchild could hang around the $250-$350 space in 2016 (especially if HBM2 is pricey), so a 6GB card slightly beneath that wouldn't look entirely out of place.

Obviously, this is speculation and I think we all look forward to seeing what the 2016 lineups look like.

 

[gamervivek]

Any estimates as to how much die area is being left on the table here. Before this, Hawaii seemed to have been the best utilization considering for about 80mm2 more it has same or even bigger advantage over Tonga compared to Fiji over it, despite the latter being about a two-fold die size difference.