Hi Xinhui,
2016-06-28 22:43 GMT+08:00 Pan Xinhui [off-list ref]:

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?

Regards,
Wanpeng Li