Strange SSD behavior!

[bathrobehero]

Hi, I'm just going to start with a picture:

screenshotuploader.com/i/01/6uu0lcv1h.png
(^sorry, can't post proper link)

Explanation:
The benchmarks on the left side are made while the CPU was not stressed, as in idle environment, but here's come the fun part because the benchmarks on the right side are made while the CPU was kept at 100% - by Everest's stress test (CPU only) but it's not exclusive to Everest, any CPU hogging application seem to make the SSD faster.


This happens both on my new Samsung 840 (non-Pro) and on my older SiliconPower V20 40GB SSD's.
Also, it's the same with both the amd_sata (1.2.1.331) and the Standard AHCI drivers.
I have an Athlon II X2 3.4 @ 4.0 CPU and a fresh Win7 x64 HP and the minimum processor state is set to 100% in the power options so it's not even about it being downclocked to around 800mhz when being idle.
My MB (M4A88T-M) only supports Sata2.


So why is my SSD is faster in every test I tried when my CPU is stressed to 100%?

[technodean]

It just looks like your cpu isn't at full speed? just did this my self @ 1600 and @ 4200.

[bathrobehero]

It is, I set that it can't downclock itself when idle.
It always looks like this:
valid.canardpc.com/2667419

[Thorsson]

Yes, CPU speed affects HDD performance. In other breaking news the Pope is discovered to be Catholic, and bear excrement is found in woods...

[bathrobehero]

First of it's exclusive to SSD's and not to HDD's and the tests were made with the same CPU with same performance. The difference weirdly comes from the CPU being stressed in any way.

[bathrobehero]

If anyone wondering I found the problem and the solution.

So apparently the CPU has more idle modes than I thought. In other words, the CPU can be idle even if it's not downclocking itself. Which is great, but some chipsets - like mine (AMD 880G/SB710) - is not "waking up" the CPU in case of heavy I/O operations.

So there's a registry key with which we can disable the cpu ever being idle by chaning the Attributes key from 1 to 0 under:
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Power\PowerSettings\54533251-82be-4824-96c1-47b60b740d00\5d76a2ca-e8c0-402f-a133-2158492d58ad]

which unlocks an option in the Power Options which looks like this:

screenshotuploader.com/i/01/in6_b5o88.jpg

So with this option I have awesome speeds - for sata2 that is - but this option has some disadvantages as well. One of which is higher CPU temperatures, more power consumption because it appears disabling this idle state is acting like the CPU is at 100% but it is not, as you can see marked on the picture with red (cpu usage).
So if you have a dumb chipset and a CPU which gets hot under heavy load than it's not for you.
My CPU's idle temperature is around 30°C with stock cooler at 10% (ten) fan speed @4.0 (from 3.4) but with this "tweak" it's around 38°C.


Source: storagereview.com/how_to_improve_low_ssd_performance_in_intel_series_5_chipset_environments

[Thorsson]

Ah OK, CPU is forced slower. Good research.