BF4 - 2GB 7870s Crossfired - AB reports 3571MB Memory usage, only ~85% GPU

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Christopher Shaffer

Christopher Shaffer

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So I have 2 7807s in Crossfire. I'm smoking it on BF4 near-Ultra and 4x MSAA, getting about 80-90FPS in campaign on average and about 60-70 in MP.

I'm on CCC 13.11 beta v1 with little to no issues, except a random crash very infrequently.

I've been running Afterburner in the background to monitor temps and have noticed two odd things:

1) As I understand it, Crossfire will only allow 1 GPU's memory to be used. I have *never* seen Afterburner report more than 2GB in use (both cards are 2GB) on *any* game until now. BF4 consistently reported ~3570MB for over an hour of gameplay.

So what's up? Is it somehow magically taking advantage of both cards' memory, or is this some fluke?


2) GPU1 and GPU2 usage % show *identical* percentages at every point in the AB log, which is odd because on every other game, they will fluctuate a bit, with GPU1 being at say, 99% when GPU2 is only at 75%. In BF4, they are matched 100% of the time.

On top of that, the max usage never passed 85%

I've been monitoring my Crossfire setup like a hawk while I've made some changes to drop temps and I've NEVER seen a game give these results. Both seem positive, so I have no complaints, but they also seem too good to be true.

Theories?
 
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cuecuemore

cuecuemore

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1) It does take advantage of the memory on both cards, it's just not additive. Afterburner reports memory usage on AMD cards as the sum of both cards, so you're using ~1800MB/card, which is consistent with everything we've seen about BF4 VRAM usage.

2) This most likely means that BF4 is doing it right. I've seen some games pace CF usage perfectly and others not do so well.

"On top of that, the max usage never passed 85%"
Unless you're above 1080p, I wouldn't expect them to... are you V-Synced?
 
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Christopher Shaffer

Christopher Shaffer

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No not using vsync. I don't have any major issues with tearing so I haven't enabled it.

The thing is ALL other games report 2GB of memory usage, not ~3500.

So are you saying they're only using about 1/2 the memory from both cards?

If its not additive the it should only report about 2GB as each card is 2GB.
 
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cuecuemore

cuecuemore

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That's because all of the other games use 2GB of RAM (or 1 on each card) and not 3.5. Many games still use less than 1GB on each card at 1080p, but remember that BF4 is our first taste of "next-gen". So each card is holding essentially the same thing in its frame buffer, and not half of one big pool of info. I don't know why Afterburner does it that way (adds the individual cards together), but it's been that way with AMD/ATI for as long as I can remember. So yes, that's what it should do, but it's dumb.
 
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iam2thecrowe

iam2thecrowe

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In crossfire each card is rendering a frame alternately and each card is working on an entire frame individually, so you only have an effective vram of 2gb, one card can't use the memory on the other card. The frames then interleave together at the output to your monitor. msi afterburner is just measuring the combined vram useage of both cards instead of showing a separate amount for each card. If you disable crossfire you would see exactly half of the memory usage compared to crossfire.
 
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Christopher Shaffer

Christopher Shaffer

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Yes, I understand this is how it is supposed to work, but there are games capable of using more than 2GB of vram if its there (like FC3) but they don't report like this on AB. If this was just AB reading both cards memory usage, the even a game that only takes advantage of 1.5GB it would report as 3GB in AB, but that's not the case.

Your explanation doesn't address the fact that Afterburner is showing that during BF4 play I'm USING 3.5GB.

When I play FC3, it might report around 1.8GB, so by this logic, the game is only taking advantage of about 900MB of VRAM. This doesn't make sense.
 
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Christopher Shaffer

Christopher Shaffer

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I'm not worried its wrong; I'm interested that it may be right.

BF4 uses Mantle, so I'm wondering if it is somehow able to make better use of the memory.

For a top-end game, latest graphics engine, I'm getting nearly 100FPS in campaign and around 80 in MP on Ultra.

That's insane.
 
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iam2thecrowe

iam2thecrowe

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bf4 does not use mantle yet, just fyi. Mantle update is later in the year. Your performance is about right, i get about the same with my cards, which perform similar to your 7870's (although i have vsync locked to 60fps as pointless going over on a 60hz monitor). My cpu is more of a limitation in multiplayer (64 player map) than my gpu's are. I have only tested with the beta game, i don't think ill buy the game, its not that good, much the same as bf3, and i'm bored of that.
 
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bassybekx

bassybekx

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srry to jump in this thread but im running 2 7850s now atm i can max out @ 50-60fps but i dont i prefer the 120fps with the resolution scale turned up a tad .. question is:

gpu-z states that im only using 1400-1600 ram that on card 1 when i switch to card 2 there is nothing to state the memory as in gpuz simply doesnt show the usage it shows clock speed, memory speed, fans, temp all that but not the dynamic or dedicated memory usage? 1. is there anyway i can check this and 2. anyone know why it does this? in fact its always showing 0 for the the dedicated and thats both cards when i disable CF
 
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Christopher Shaffer

Christopher Shaffer

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This is an issue that crops up due to something w/the AMD driver. GPU-z is having issues getting the reading somehow.

MSI Afterburner usually works fine for this.
 
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