[parisc-linux] ldcw in __pthread_acquire

[Philippe Benard]

> >
> > Note also that spinning in a ldcw is very painful for the bus, and
> > switching to a ldw-loop followed by ldcw results in starvation in a
> > greater-than-2-way MP system.
> 
> That sounds a good reason to do at least most of it in kernel space on hppa
> 


I think LaMont Jones meant that the spinlock loop (in user space AND in kernel
space) must implement a load word loop, and issue a load-and-clear word only
when the lock word looks 'free', this is because the 'write' part of the
load-and-clear word issue a cache broadcast transaction on the bus, so the
loop should be on load-word followed by load-clear-word when it looks free,
after a given amount of loop you got to ask for kernel arbitration, then OS
whence again try to get the lock and if fail go to sleep.

Phi