Hi Marcus,
thank you very much for you fast and detailed answer! Overall this should be really helpful for reconstructing what changes need to be done.
I would be very interested in the results of your measurements! Do you already have other libpthread implementations in mind that you want to look at? As noted in the BENCHMARKING file in l4re (https://github.com/kernkonzept/mk/blob/master/BENCHMARKING) a heads up to benchmarking@os.inf.tu-dresden.de on any measurements before they are published would be highly appreciated so that we can sanity-check them and if they match our experience with the performance we see.
I already read this file before and will do so. If I got some results, or any questions for that matter, I'll respond to this thread again (regarding results more likely after sending them to benchmarking@os.inf.tu-dresden.de first).
Thanks again!
Best regards
Pascal
On 1/24/24 20:54, Marcus Hähnel wrote:
Hi Pascal,
On 2024-01-24 12:53, Pascal Scholz wrote:
- Is there a technical reason for L4Re still using the Linuxthreads
implementation and not some kind of NPTL port or other implementations?
The libpthread implementation used in L4Re is based on the linuxthreads (formerly named linuxthreads.old) implementation from uClibc. There is no particular reason why one was chosen over the other that I am aware of. In the end it doesn't matter that much, since the "backend" is highly L4 specific anyways. I guess the linuxthreads implementation was easier to port.
- What uClibc is used exactly? Do you manage your own fork of uClibc
and back port relevant patches of uClibc-ng? Or do you use a uClibc-ng with additional L4 patches? Or some completely other version? It seems that the uClibc version used diverged in 2014 from the original. This seems relevant to me as I wanted to check, which changes were done to make the uClibc work with L4 (in an attempt to generate some kind of a diff), so I might port them to another libc implementation.
Originally uClibc was used and adapted to L4Re. When uClibc was no longer actively maintained we implemented some of the things we needed ourselves or ported them from other C libraries. After uclibc-ng gained traction we started first porting fixes and improvements from them when we needed them. More recently we started to synchronize uClibc with the current upstream uClibc-ng state and also already contributed some of our changes back where this made sense to us. This is not yet done but a work in progress and you will likely see more changes to our uClibc during the next months.
In my project I would like to replace Linuxthreads with some other pthreads implementation and measure the performance impacts of these changes, so the aforementioned questions seem relevant to me.
The best start is probably to to look at the libpthread implementation you find in l4re-core/uclibc/lib/libpthread and compare this to the upstream/uclibc-ng version of these files. Though the upstream might have diverged in the meantime. We only imported changes when they were known to be performance critical or bug fixes but otherwise kept our implementation stable so far. This might as well change once we caught up with upstream uclibc-ng.
I would be very interested in the results of your measurements! Do you already have other libpthread implementations in mind that you want to look at? As noted in the BENCHMARKING file in l4re (https://github.com/kernkonzept/mk/blob/master/BENCHMARKING) a heads up to benchmarking@os.inf.tu-dresden.de on any measurements before they are published would be highly appreciated so that we can sanity-check them and if they match our experience with the performance we see.
If you have any questions while looking at the code don't hesitate to ask.
Best regards and happy hacking!
- Marcus
Thanks in advance for you time!
Kind regards,
Pascal
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