Poor SSD performance on DM8148

Vitaly Makarov

Dear All,

I am testing SSD drive performance connected to DM8148. In my setup I use DM8148 EVM and OCZ Vertex 3 SSD drive, u-boot and Linux kernel are from PSP_04_04_00_02.

SSD drive is detected as SATA-2 device, link stays in SATA-2 mode, I do not see any errors. IO scheduling is disabled.

For the test I use something like the following command: "time dd if=/dev/null of=/dev/sda bs=1M count=5120"

On DM8148 after multiple repetitions the average speed is approximately 95MB/s.

The same drive on my Linux workstation with the same test shows 200+ MB/s.

What is the reason for such a difference in performance? Is it the hardware limitation? If not, how to improve it?

Thank you for any suggestion

over 13 years ago

0 Renjith Thomas over 12 years ago

Guru 31670 points

Vitaly,

Can you check the kernel logs to see whether SATA is clocked at 1.5Gbps or 3 Gbps?

0 Vitaly Makarov over 12 years ago in reply to Renjith Thomas

Prodigy 140 points

Hi Renjith,

It is definitely 3.0Gb/s:

ata1: SATA link up 3.0 Gbps (SStatus 123 SControl 300)

Regards,

Vitaly

0 Renjith Thomas over 12 years ago in reply to Vitaly Makarov

Guru 31670 points

Vitaly,

What ever performance that you are getting is in-line with TI's PSP release performance parameters.

http://processors.wiki.ti.com/index.php/DM814x_AM387x_PSP_04.01.00.07_Feature_Performance_Guide#SATA_-_ext2_File_System_Performance

But in my opinion there is more room for optimizing the driver and can achieve somewhere close to 150MB/sec.

BTW, what is your application's actual throughput requirement?

0 Vitaly Makarov over 12 years ago in reply to Renjith Thomas

Prodigy 140 points

Renjith,

Our target speed is ~120MB/s

Please note, that my dd test shows "ideal" performance, in real life applications the number will be probably around 80% of it.

If you think that 150MB/s is possible, what kind of optimization could be done here?

Thank you,

Vitaly

0 Renjith Thomas over 12 years ago in reply to Vitaly Makarov

Guru 31670 points

Vitaly,

150MB/sec using dd should be possible in my opinion. The optimization includes overall system tuning, DDR performance, DMA code optimization and improving interrupt latencies etc.. Before arriving at the exact solution, we need to analyze where is time being wasted and how can we improve. So, basically more analysis needs to be performed first.

Processors

Processors forum

Poor SSD performance on DM8148