Re: [PATCH 1/2] kernel/sched: introduce vcpu preempted interface

[xinhui]

On 2016å06æ27æ 16:42, Peter Zijlstra wrote:
> On Sun, Jun 26, 2016 at 06:41:54AM -0400, Pan Xinhui wrote:
>
> > +#ifdef arch_vcpu_is_preempted
> > +static inline bool vcpu_is_preempted(int cpu)
> > +{
> > +	return arch_vcpu_is_preempted(cpu);
> > +}
> > +#else
> > +static inline bool vcpu_is_preempted(int cpu)
> > +{
> > +	return 0;
> > +}
> > +#endif
> > +
> > +#ifdef arch_vcpu_get_yield_count
> > +static inline unsigned int vcpu_get_yield_count(int cpu)
> > +{
> > +	return arch_vcpu_get_yield_count(cpu);
> > +}
> > +#else
> > +static inline unsigned int vcpu_get_yield_count(int cpu)
> > +{
> > +	return 0;
> > +}
> > +#endif
>
>
> Please, just do something like:
>
> #ifndef vcpu_is_preempted
> static inline bool vcpu_is_preempted(int cpu)
> {
> 	return false;
> }
> #endif
>
> No point in making it more complicated.
right, vcpu_is_preempted() is good enough to handle our osq issue.

> > +static inline bool
> > +need_yield_to(int vcpu, unsigned int old_yield_count)
>
> namespace... this thing should be called: vcpu_something()
>
> > +{
> > +	/* if we find the vcpu is preempted,
> > +	* then we may want to kick it, IOW, yield to it
> > +	*/
> > +	return vcpu_is_preempted(vcpu) ||
> > +		(vcpu_get_yield_count(vcpu) != old_yield_count);
> > +}
>
> And can you make doubly sure (and mention in the Changelog) that the OSQ
> code compiles all this away when using these definitions.
vimdiff shows the osq_lock.o has a little difference because osq read the yield_count and prev, even they are not used.

however, as you suggest above, IF I remove the vcpu_get_yield_count() and relevant code in osq_lock,  then the binary is same.