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SubjectRe: 2.6.13-rc6-rt9

* 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
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