[9front] Re: devfs performance

[Martijn Heil <m.heil375@gmail.com>]

In the meantime I've started writing an (experimental) patch for
devfs, that should at least work for my use if I succeed. I'll gladly
share it if I consider it anywhere near worthy, but considering my
inexperience with this kernel development I have no expectations.
Nonetheless I'll try my best.

In case anyone is interested in the technical details;
Block-interleaved I/O is handled by interio() at /sys/src/9/port/devfs:1134.
This in turn synchronously calls the blocking io() located at
/sys/src/9/port/devfs:1031 for each sequential block to read from the
inner devices.
My idea so far is to have one kproc worker per inner device which will
communicate with the interio() function by the use of two Qio queue's:
one for sending read/write requests to the worker and the other for
sending results back from the worker to interio(). The workers will
then call io() as requested, which of course, will block the worker.
I'm debating whether I should have those live for the duration of the
life of the fsdev device, or whether I should spin them up on-demand.
I think the best option is to have them live for the duration of the
devfs device, so that the overhead of spinning up several kprocs for
every little read and write can be avoided, in turn for some slight(?)
extra memory usage that the idle kprocs will take up.

Again, I have no experience in this and no real expectations either.
Maybe I'm trying something really stupid.
Please feel free to correct.
It's certainly fun and educational.

I'm really interested in any other suggestions on how to do this properly.

Regards,
Martijn Heil
aka
ninjoh