topic [iMX6Q] Poor SATA Write Performance in i.MX Processors

[iMX6Q] Poor SATA Write Performance

davidmüller — Sat, 10 Oct 2015 05:48:50 GMT

Hello

I have an i.MX6Q based SabreSDB running Freescale kernel 3.14.28, alternatively a home-brew vanilla 4.1.0 kernel.

All four cores running at 996MHz, "cpufreq" set to "performance".

Using a SATA-to-CFast adapter and a SATA-II capable CFast card, I tested the SATA write perfomance of the i.MX6Q.

To simulate a "real-life" situation (with all the system overhead included), I created a shell script which copies the same file (10MiB in size) 20 times (using different target names) from a ramdisk to a 1GiB VFAT partition on the CFast card.

The time is stopped once the final "sync" returns ensuring all the internal buffers are flushed.

Above test sequence results in a SATA write speed of at most ~50MiB/s.

I also tried an Intel 330 Series SSD attached directly to the SATA port of the SabreSB port, but the result is more or less the same.

The same test done on Intel based systems (using vanilla 3.14.28 and 4.1.0 kernels) results in SATA write speeds of up to ~130MiB/s therefore it seems that the i.MX6 itself (hardware and/or software) is the limiting factor.

What "real-life" SATA write speed could I expect from a i.MX6Q based system?

Are there any bandwidth limitiation in the SATA area of the i.MX6, similiar to the limitation of the FEC?

Does anybody have some comparative values from similiar "real-life" applications?

Or is the ~50 MiB/s already the upper limit for an i.MX6Q based system?

Re: [iMX6Q] Poor SATA Write Performance

igorpadykov — Mon, 12 Oct 2015 03:55:16 GMT

Hi David

75 MB/s was obtained on ARM2 validation board (ER3 release, DVFS off),

which close to your results.

Best regards

igor

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Re: [iMX6Q] Poor SATA Write Performance

davidmüller — Wed, 14 Oct 2015 10:49:27 GMT

Dear Igor

Thank you for your information.

What puzzles me is the fact the reading from the same CFast card is around twice as fast as writing.

Do you have an idea what could cause this asymmetry in read/write performance?