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Re: mutexes, IPL, tty locking
> On Thu, Oct 22, 2009 at 12:32:12PM +0100, Mindaugas Rasiukevicius wrote:
> > IPL is only being raised and that works in reference counting principle.
> > Therefore IPL is lowered (and only to IPL_NONE) after the last release,
> > see ci_mtx_oldspl and ci_mtx_count. Which means that order of releases
> > does not matter. Gradual IPL lowering would unnecessary complicate the
> > implementation or interface.
> Not that much. Here's some strawman code based on what's in one of my
> kernels, adapted partly for NetBSD. It isn't tested (and doesn't
> compile) but the original form does of course compile, run, and work
> in its own environment.
> I'm not suggesting that we use this as such (and it would take quite a
> bit of work to merge it) but I think the general approach is worth
i don't think it's worth to do at this point because
- much complexity for little gain.
- it involves more frequent change of the effective IPL, which might
otoh, given that we have multi levels of hw interrupts, spin locks can
be nested even for not-so-poor code. it might be worth to reinvestigate
at some point later. (when more interrupt handlers get mp-safe.)
however, even if it turns out to be a problem, my bet is that moving
more work from hw interrupt to softint is a better solution.
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