Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check

[xinhui]

Hi, wanpeng

On 2016å07æ05æ 17:57, Wanpeng Li wrote:
> Hi Xinhui,
> 2016-06-28 22:43 GMT+08:00 Pan Xinhui <xinhui.pan@xxxxxxxxxxxxxxxxxx>:
> > This is to fix some lock holder preemption issues. Some other locks
> > implementation do a spin loop before acquiring the lock itself. Currently
> > kernel has an interface of bool vcpu_is_preempted(int cpu). It take the cpu
> > as parameter and return true if the cpu is preempted. Then kernel can break
> > the spin loops upon on the retval of vcpu_is_preempted.
> >
> > As kernel has used this interface, So lets support it.
> >
> > Only pSeries need supoort it. And the fact is powerNV are built into same
> > kernel image with pSeries. So we need return false if we are runnig as
> > powerNV. The another fact is that lppaca->yiled_count keeps zero on
> > powerNV. So we can just skip the machine type.
>
> Lock holder vCPU preemption can be detected by hardware pSeries or
> paravirt method?
There is one shard struct between kernel and powerVM/KVM. And we read the yield_count of this struct to detect if one vcpu is running or not.
SO it's easy for ppc to implement such interface. Note that yield_count is set by powerVM/KVM.
and only pSeries can run a guest for now. :)

I also review x86 related code, looks like we need add one hyer-call to get such vcpu preemption info?

thanks
xinui
> Regards,
> Wanpeng Li