Re: Priority Ceiling for SMP?

Luís Henriques wrote:

http://www-md.e-technik.uni-rostock.de/ma/gol/rtsys/articulos/YCS159.pdf

Thanks for this link. This paper teached me the right keywords
to feed Google and i stumbled over this one:

https://drum.umd.edu/dspace/bitstream/1903/630/1/CS-TR-3252.ps

However, it seems like this "Multiprocessor Priority Ceiling Protocol"
doesn't allow nested locking and thus is not applicable to -rt :-(

I would like, however, to add that telling "our OS avoids dead-locks by 
design" is also not enough for SIL certification -- you need to prove this,

True, but you only need to do it once for the OS and not
for all applications developed on top of it, afterwards

which might be as difficult as implementing your system without these 
mechanisms (they tend to add high complexity to the kernel).

This depends into which level of detail the SIL certifier likes
to dig :-)

BTW and just for curiosity: anyone's aware of any application running on top 
of a Linux kernel that has been SIL (or similar) certified?  I guess that you 
need a fully qualified kernel for SIL, right?

IIRC, you can claim yourself that your system reaches SIL1 or SIL2.
(it's a little bit like the "CE" sign). The fun starts at SIL3
and SIL4, where you get your system certified by somebody else.

To sum up: most of the priority-inversion/dead-lock avoidance mechanisms 
(we've been discussing PI and PC but probably there are much more...) have 
advantages and disadventages which are widely known and documented.  The 
conclusion, I guess, is that no "magic" solution exists and the applications 
system architects will need to choose one or more (or none!) of the available 
mechanisms.

Agreed.

My personal opinion is that, no matter what mechanism you select, if your 
developing critical software you will _always_ need to perform static 
schedulability analysis of your system and never rely on PI or PC.

Basically agreed, however, this can be a very challenging activity
for a highly dynamic system like Linux :-)

regards

Bernhard