DMI overclocking with BCLK possible?

[FrostigerFinger]

I'd like to know if it is possible to increase the DMI bandwidth on a P55 board (ASUS P7P55D-E) by increasing the BCLK.

The reason for this is my plan to use an m2 NVMe SSD in my second PCI-e x16 slot (only 4 PCI-e 2.0 lanes available) with an m2 to PCI-e adapter.

Now, the problem with the P55 chipset seems to be that it bottlenecks itself hard with a DMI bandwidth of only 2.0 GB/s. That appears to be the reason why the PCI-e 2.0 lanes only operate at 2.5 GT/s (PCI-e 1.x speed).

With everything left at stock that would probably slow down a modern SSD to 1000/1000 MB/s read/write.

Would the DMI bandwidth increase with a higher BCLK or is it independent?
Could that improve the read/write speed of the SSD?

Is all of this bullshit? If yes, please feel free to enlighten me 😉

 

[Insert_Nickname]

Is all of this bullshit? If yes, please feel free to enlighten me 😉

As a general rule, its a bad idea to touch BCLK. Especially on LGA-115x platforms. The reason is that everything is running of it, from your SATA controller to USB ports. Everything gets overclocked.

Since you only have a PCIe 2.0 x4 slot available, you're not going to get more then 1600'ish MB/s through it anyway. The DMI 2.0 interface tops out thereabouts, OC or no OC. An OC like you're thinking might add a 100MB/s, not really worth the trade-off in reliability in my opinion.

Another thing you'll run into is booting from the PCIe SSD. Most, if not all, LGA-1156 boards use an old fashion BIOS. Not UEFI which is required for NVMe support. Further, since your BIOS lacks NVMe support, the PCIe drive needs to provide its own OROM for booting. This in effect leaves you with two choices, either the Plextor M6e (if you can find it) or the Kingston HyperX Predator.

I'm sorry to pull the plug on your plans like this, but you're much better of with a high performance SATA drive, like the Samsung 850PRO, which is guaranteed compatible with your system as is. You're very unlikely to feel any improvement from an NVMe drive outside benchmarks. 🙂

 

[FrostigerFinger]

As a general rule, its a bad idea to touch BCLK. Especially on LGA-115x platforms. The reason is that everything is running of it, from your SATA controller to USB ports. Everything gets overclocked.

Since you only have a PCIe 2.0 x4 slot available, you're not going to get more then 1600'ish MB/s through it anyway. The DMI 2.0 interface tops out thereabouts, OC or no OC. An OC like you're thinking might add a 100MB/s, not really worth the trade-off in reliability in my opinion.

Another thing you'll run into is booting from the PCIe SSD. Most, if not all, LGA-1156 boards use an old fashion BIOS. Not UEFI which is required for NVMe support. Further, since your BIOS lacks NVMe support, the PCIe drive needs to provide its own OROM for booting. This in effect leaves you with two choices, either the Plextor M6e (if you can find it) or the Kingston HyperX Predator.

I'm sorry to pull the plug on your plans like this, but you're much better of with a high performance SATA drive, like the Samsung 850PRO, which is guaranteed compatible with your system as is. You're very unlikely to feel any improvement from an NVMe drive outside benchmarks. 🙂

Thanks for the response!
I've been running the BCLK at 170 for over 6 years now and there was no problem whatsoever. I seem to recall that BCLK overclocking only caused problems on SandyBridge and later CPUs.

You don't happen to know why the P55 chipset limits the PCI-e speed of the chipset to PCI-e 1.x speed if the DMI is not the problem, do you?

I know about the boot issue, but that's no problem since I'll simply use my existing sata ssd for windows and the m2 ssd for programs I use regularly.

My piece of shit of a mainboard has one of those marvellous sata 3 controllers, if you know what I mean 😀.
Meaning the Intel sata 2 controller on the board is faster ...
Even if the PCI-e slot only operates with 4 PCI-e 1.1 lanes, that should still be more than 3 times as fast as my current ssd.
And I can re-use an NVMe SSD with a new system that's to be mine within the next year.

 

[Insert_Nickname]

I've been running the BCLK at 170 for over 6 years now and there was no problem whatsoever. I seem to recall that BCLK overclocking only caused problems on SandyBridge and later CPUs.

You're right. I mixed up the LGA-1156 platform with LGA-1366 platform, and the BLCK "issue" was only SB and newer. Oh well, can't win them all. 😕

Nehalem used the original DMI link. Which means a lazy 1GB/s in both directions. Which in practice properly means a max of 700MB/s sequential. Random I/O isn't as affected by SATA link speed BTW, so a newer SATA3 SSD will only be limited in sequential R/W throughput.

You still can't boot from an NVMe drive though. Used as a data drive should be fine however.