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Memory clock speed: 800MHz vs 1600MHz? (NM, RK3399 won't run >800MHz DDR)
Syonyk
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06-23-2020, 01:38 PM (This post was last modified: 06-23-2020, 02:04 PM by Syonyk.)
Sorry for what I hope is a stupid question...

I'm running a Pinebook Pro with the "mrfixit BSP uboot" - for deep sleep and such.

I'm using the Manjaro/tsys 5.7 kernel with hwaccel patches.

Uboot log:
Spoiler:



What I'm interested in, though, is the memory training speed.

Code:
channel 0 training pass!
channel 1 training pass!
change freq to 800MHz 1,0
Channel 0: LPDDR4,800MHz
Bus Width=32 Col=10 Bank=8 Row=15/15 CS=2 Die Bus-Width=16 Size=2048MB
Channel 1: LPDDR4,800MHz
Bus Width=32 Col=10 Bank=8 Row=15/15 CS=2 Die Bus-Width=16 Size=2048MB
256B stride

This is the final training pass I see in the uboot output.

Looking at the datsheet, the memory modules are either rated for 1600MHz or 1866MHz.

I've found that the RK3399 supports dynamic DRAM frequency scaling, but I haven't verified if this is working - I don't see anything about it in dmesg.

I see a peak of about 5.5GB/s running the "mbw" benchmark.  At 800MHz on a 64 bit bus, I'd expect (800 * 2 * 64 / 8) = 12.8GB/s, which is consistent with a streaming copy bandwidth of around 5.5GB/s.

At 1600MHz, I'd expect to see 25.6GB/s - and I know there's display overhead, but for an optimized copy, it seems like we're not seeing the full performance of this system.

So, my questions:

0. Am I misreading the output/screwing up my math?
1. How can I verify the memory frequency in Linux?
2. Should uboot be setting the frequency to the maximum before handing off to a kernel that might not be adjusting it?
3. Should we have dynamic memory frequency stuff enabled in the kernel?

Thanks!
Well, darn.  I was looking at the LPDDR4 datasheet, should have been looking at the RK3399 datasheet.

Per IRC, it just doesn't support running the memory bus up that high.  Seems to be limited at 933 for DDR3, 800 for DDR4.

Was a good question, I suppose.
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Messages In This Thread
Memory clock speed: 800MHz vs 1600MHz? (NM, RK3399 won't run >800MHz DDR) - by Syonyk - 06-23-2020, 01:38 PM

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