Shortly after publishing A Messy Transition (Part 1) we received numerous requests for similar user address space usage testing under Windows XP, as we had previously done all of our testing on our standard Windows Vista setup. Although we were not expecting a great difference - certainly Vista will use more resources than XP because it's a newer and heavier operating system - we decided to follow these requests anyhow. However what we found completely blew our expectations.

And with that said we'll immediately dive in to the results of our findings. We'll be picking up from where we left off, so please read part 1 if you haven't already.

Software Test Bed
Processor AMD Athlon 64 4600+
(2x2.4GHz/512KB Cache, S939)
RAM OCZ EL Platinum DDR-400 (4x512MB)
Motherboard ASUS A8N-SLI Premium (nForce 4 SLI)
System Platform Drivers NV 15.00
Hard Drive Maxtor MaXLine Pro 500GB SATA
Video Cards

1 x GeForce 8800GTX
1 x GeForce 7800GTX(256MB)
1 x Radeon X1900XTX(512MB)

Video Drivers NV ForceWare 163.11(Vista)
NV ForceWare 162.18(XP)
ATI Catalyst 7.6
Power Supply OCZ GameXStream 700W
Desktop Resolution 1600x1200
Operating System Windows Vista Ultimate 32-Bit
Windows XP Professional SP2
.

The principles of address space allocation and usage are virtually the same between Vista and XP, so as with our Vista tests we first attempted to crash Supreme Commander against a modified 2.6GB of user address space. Because this needed to be repeatable we have switched to using replays instead of a live game, but the goal remains the same one of monitoring memory usage and looking for Supreme Commander to crash. Or surprisingly, to not crash; we were unable to make Supreme Commander crash and not for a lack of trying.

Supreme Commander Address Space Usage
(GeForce 8800GTX, 768MB)
Game Start Replay Start Replay End
Windows Vista 562MB 1.21GB 1.95GB
Windows XP 116MB 930MB 1.44GB
.

The above is a chart of the user address space usage of Supreme Commander when the application was launched, at the start of the replay, and 15 minutes in to that replay. Although using a replay reduced overall address space usage (which is why not even Vista is above 2GB at 15 minutes in), there is a massive difference in usage between XP and Vista at all points. At the start of the replay there's already a 300MB difference in address space usage, and by 15 minutes in when Supreme Commander is heavily loaded down that difference has ballooned to 500MB, a full 25% of the total address space the application gets under normal circumstances.

Appropriately, the difference in address space usage was the reason that Supreme Commander would not crash under XP like it would under Vista. Address space usage peaked at 2.1GB, which while in excess of the default 2GB barrier is below the 2.6GB mark where it crashed under Vista. Even a slight reduction in address space usage here would have kept the game from hitting the 2GB barrier at all, avoiding the whole can of worms that is modifying the user address space allocations.

Supreme Commander Address Space Usage
(Radeon X1900XTX, 512MB)
Game Start Replay Start Replay End
Windows Vista 230MB 1.15GB 1.87GB
Windows XP 124MB 939MB 1.44GB
.

As we originally had a suspicion that this could be related to NVIDIA's drivers, we swapped out our 8800GTX for a 512MB Radeon X1900XTX and ran the Supreme Commander tests under both Vista and XP. The results were virtually identical with Supreme Commander consuming more address space under Vista than XP. Curiously however the overall amount of address space used by Vista is down slightly (by about 120MB) compared to the 8800GTX.

Supreme Commander Address Space Usage
(GeForce 7800GTX, 256MB)
Game Start Replay Start Replay End
Windows Vista 240MB 1.10GB 1.75GB
Windows XP 119MB 928MB 1.43GB
.

In trying to explain the difference in address space usage under Vista, we finally pulled out a 256MB GeForce 7800GTX. What we found was that the gap between Vista and XP remains, but it is smaller yet again as Vista's address space usage shrunk another 120MB compared to the 512MB Radeon card. With the above numbers we can definitely say there appears to be some sort of relationship between address space usage and video memory under Supreme Commander. But this also raises the question: is this difference in usage of our increasingly critical address space a function of Windows, or something specifically related to Supreme Commander?

A Second Opinion
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  • EndPCNoise - Saturday, July 21, 2007 - link

    On another note...Why does Microsoft state that 32-bit Vista Home Premium supports up to 16GB RAM if there still exists a 4GB limit on address space? -- This does not make sense.

    Ignore this part in the above post. It is a mistake. All 32-bit versions of Vista have the 4GB limit on address space, which would make sense.

    The 64-bit Vista Home Premium has an address space limit of 16 GB.
    Reply
  • saratoga - Thursday, July 19, 2007 - link

    I doubt you'll see a "fix" since this really isn't a bug. Its just the limits of whats possible in a 32 bit system. The solution is going to be Vista 64.

    Regarding the difference in VM space, I'd assume this is DX10 at work. It doubtless requires more VM space (if not more memory), so I'd expect to see a big difference between Vista and XP.
    Reply
  • Ryan Smith - Thursday, July 19, 2007 - link

    Close, it's DX9Ex and the new WDDM at work. The Vista DX9 implementation has a few more "features" as a result of the WDDM. Reply
  • imaheadcase - Thursday, July 19, 2007 - link

    They could easily test if it is a DX10 issue by testing CoH, it ha DX9 or DX10 Reply
  • smitty3268 - Thursday, July 19, 2007 - link

    Sort of. They'd actually still be testing the DX10 code in Vista, though, just running the old DX9 compatibility path through it. I'm not sure you can really conclude anything from that or not, although it would be an interesting test to see. Reply
  • mlau - Thursday, July 19, 2007 - link

    Supcom probably brings the windows VM to it's knees, and since programmers
    are a lazy bunch (I know I am) and usually don't check for failed memory
    allocations (and the error paths are almost NEVER exercised during testing),
    supcom crashes. You can paper over this by adding a few more gigs of ram,
    but it's no excuse for app stupidity.
    Reply
  • smitty3268 - Thursday, July 19, 2007 - link

    quote:

    You can paper over this by adding a few more gigs of ram,


    Actually, the whole point is that adding more RAM doesn't help. Due to the nature of 32-bit OS's, virtual memory is capped to 4GB and most OS's limit it to 2GB for user applications. This limit doesn't change whether you have 256MB of physical memory or 4GB. You're right about the testing, though - most programmers just assume that memory is unlimited and don't think about checking to make sure an allocation didn't fail.
    Reply

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