Recommend isal on PyPy and aarch64 platforms

[rhpvorderman]

I did some benchmarks on my olimex olinuxino A64 with allwinner A64 chip. (AArch64 architecture). This was to ascertain the performance of python-zlib-ng. I also took python-isal into the comparison.

It appears that isal and zlib-ng do not speed up decompression, but both do speed up compression. In fact, isal is three times faster at the levels it supports.

I removed aarch64 support once: #79. But that was before I made python-isal into a C-module. Apparently the Cython module had some performance issues on aarch64. Luckily isal and zlib-ng python modules are both implemented in C now.

This is a quick and easy PR. I guess I should add zlib-ng now.

As for PyPy, I do run the full test suite and it works. Generally PyPy is very slow in calling C-extensions, but that is an overhead that applies equally to all deflate libraries.

[marcelm]

Quick and easy indee. Thanks for the investigation. I think these little tweaks are what makes this makes this project worthwhile.

Thanks for the pointer to the olinuxino, I had not heard about it. Maybe time to get one while the RasPis are still out of stock everywhere.

[rhpvorderman]

Thanks for the pointer to the olinuxino, I had not heard about it. Maybe time to get one while the RasPis are still out of stock everywhere.

I have to note that the allwinner A64 has a hardware bug(!) where the platform will be unstable if run at varying clockspeeds. So you would have to run it at a fixed clockfrequency. I run it in "powersave" mode. It cannot idle (unfortunately) and consumes 2.4 watts constantly. I am fine with that, but it is something to keep in mind.

I found olinuxino trough this page on the debian wiki: https://wiki.debian.org/CheapServerBoxHardware
There might be some other boards that are interesting for your use case.

[marcelm]

Thanks!