Re: [PATCH V2 0/6][RFC] futex: FUTEX_LOCK with optional adaptivespinning

[Avi Kivity]

On 04/06/2010 10:31 PM, Thomas Gleixner wrote:
> > That gives you something along the lines of
> >
> > 	runaddr = find_run_flag(lock);
> > 	do {
> > 		while(*runaddr == RUNNING) {
> > 			if (trylock(lock))
> > 				return WHOOPEE;
> > 			cpu relax
> > 		}
> > 		yield (_on(thread));
> >      
> That would require a new yield_to_target() syscall, which either
> blocks the caller when the target thread is not runnable or returns an
> error code which signals to go into the slow path.
>    

Note, directed yield is something that kvm wants for its own ends.  As 
an internal kernel api, not a syscall, but it's apparently useful.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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