[Situation improved] PSA: S905X cpu is significantly slower than S905 cpu

Hello,

in the datasheets and comparisons from amlogic and third-party websites, the SoCs 905 and 905X look very similar: They both have a "Quad core Cortex A53 @ 2.0 GHz" (or 1.5 GHz, if the sheet was fixed after the shady frequency scaling of the amlogic kernel came to light) and a "Penta-core ARM Mali-450MP" GPU. The main difference that is noted are the different video codecs that are supported by the hardware: S905X adds VP9 and HEVC Main10 with HDR decoding and the neccessary HDMI 2.0b link.

Last week I received a S905X box and did some comparisons. While both worked fine with libreelec, and hardware decoded video was the same; software decoded video showed significant differences: S905 would play 720p h.264 10-bit ("hi10p") encoded videos just fine, while S905X would not be watchable at all: video was jerky, with many dropped frames and severe a/v sync issues.

The reason appears to be a difference in the cpu cores: During playback, the S905 was at less than 80% load per core, while the S905X was at 100% load. Further searches found that benchmarks under android also show a difference between S905 and S905X. See Amlogic S905 vs S905X Benchmarks Comparison

Conclusion: If you are interested in cpu-bound applications on your device, like software decoded video, emulation and games, pick the S905 over the S905X.
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Update 2017/03/17: With version 8.0.0f the S905X can keep up with 720p h264 10bit software decoding.

Kernel is always 64 bit. I compared in 32 bit userland.

In earlier tests, S905 64 bit userland compared to 32 bit userland was no change for software decoder cpu load.

Interesting, I had absolutely no difference in hardware decoded playback. I tried several files I made with makemkv from my BD collection.

What kind of problems did you have with high bitrate videos on S905?

Those work until the network interface becomes the bottleneck.

Quote from Ftelf

mmpp What was the sustained temperature of the cpu during the evaluation ? Quality of the CPU cooler on those box vary a lot. One had a tiny 10x10x5mm one, which would barely cool a memory chip, the other 25x25x10mm. Once the cpu temp went up, it is a one-way (throttling-lagging-100%-cpu-usage).

To limit the effect of overheating, I compared the playback immediately after I started both boxes. From the first second, the S905x cannot keep up decoding the files and CPU is at 100%.

CPU and DRAM clock speeds are setup by the early-stage boot process. There is some information on the odroid forum (where they found out about the fake frequency settings in the kernel) but I have no idea if or how one can replace the mentioned files on generic tv boxes.

You can read about the odroid c2 "over"clocking here: ODROID Forum • View topic - No performance difference between 1.5, 1.75 & 2GHz

I usually do not crosspost but as some might find this thread by search, I want to note the current development here as well:

Quote from kszaq

It's been a quiet week for LE 8.0 and Kodi 17 so let's break something.

8.0.0f posted in OP with an experimental change to HW decoder that might improve seek and channel switching times - please report if they're better, worse or the same. There is also a performance bump for S905X (it's still a bit slower than S905 but the gap is now much smaller) and improvement to Bluetooth audio. Enjoy!

I can confirm that software decoded playback of 720p h264 10bit videos, which was dropping a lot of frames on S905X and worked fine on S905 on earlier versions has improved on S905X. I only tried a few files and currently cannot do side-by-side comparisons, but the tested files were watchable. Big thumbs up to kszaq for this "bump".

I am very happy to update this old thread: with the latest "full nougat" kernel developments by kszaq and johngalt, the gap between S905x and S905 performance has been reduced even further.

My S905x box can now flawlessly software decode several cpu-intensive 720p hi10p files from my collection that I had earmarked when I did the comparison earlier this year.