Re: 2.6.13-rc6-rt9

[Ingo Molnar <mingo@elte.hu>]

* Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 2005-08-23 at 14:36 +0200, Ingo Molnar wrote:
> > * Steven Rostedt <rostedt@goodmis.org> wrote:
> > 
> > > Ingo, can't you get rt.c to be more confusing. I mean it is too 
> > > simple. We need to add a few more underscores here and there :-) 
> > > Seriously, that rt.c is mind boggling. It was nice before, now it is 
> > > just screaming for a cleanup (come now, do we really need the four 
> > > underscores?). Same with latency.c.
> > 
> > i agree that it's ugly, but some of that ugliness is to achieve the 
> > 7-instructions fail-through codepath for the common acquire (and 
> > release) codepath:
> > 
> >  c03a5320 <__down_mutex>:
> >  c03a5320:       89 c1                   mov    %eax,%ecx
> >  c03a5322:       8b 15 08 76 3a c0       mov    0xc03a7608,%edx
> >  c03a5328:       31 c0                   xor    %eax,%eax
> >  c03a532a:       0f b1 51 14             cmpxchg %edx,0x14(%ecx)
> >  c03a532e:       85 c0                   test   %eax,%eax
> >  c03a5330:       75 01                   jne    c03a5333 <__down_mutex+0x13>
> >  c03a5332:       c3                      ret
> > 
> 
> Impressive!
> 
> > that's how much it takes to acquire an RT lock, and i worked hard to get 
> > there. As long as the fastpath is kept this tight, feel free to do 
> > cleanups. But i really want to avoid having to write mutex_down/up in 
> > assembly for 24 architectures ...
> 
> Warning! I'm hacking hard to get rid of the global pi_lock, and I'm not
> worrying now about efficiency.  I figure that if I can get it to work,
> then we can speed it up afterwards.  Since it's complex enough keeping
> all the locks straight, I just want it to work without deadlocking. 
> 
> Once I get it to work, I'll let you figure out how get it back down to 
> 7-instructions :-)

yeah. It can always be done after the fact - the basics wont change.  
(Note that the above disassembly is for UP, on SMP the fastpath is 
longer and around 10-15 instructions.)

	Ingo