Hi, On 18-09-17 20:54:52, Yi Sun wrote: > On 18-09-14 12:42:33, Thomas Gleixner wrote: > > On Fri, 14 Sep 2018, Yi Sun wrote: > > > > > +static void hv_notify_long_spin_wait(void) > > > > > +{ > > > > > + u64 input = spin_wait_info | 0x00000000ffffffff; > > > > > > > > What? The result is always 0x00000000ffffffff ..... > > > > > > > Oh, sorry for such error. > > > > > > > > + spin_wait_info++; > > > > > + hv_do_fast_hypercall8(HVCALL_NOTIFY_LONG_SPIN_WAIT, input); > > > > > +} > > > > > + > > > > > +static void hv_qlock_kick(int cpu) > > > > > +{ > > > > > + spin_wait_info--; > > > > > > > > Looking at the above this is completely pointless and I have no idea > > > > what > > > > that variable is supposed to do. > > > > > > > Per Microsoft Hypervisor Top Level Functional Specification, the input > > > parameter of HVCALL_NOTIFY_LONG_SPIN_WAIT is defined as below: > > > > > > SpinwaitInfo – Specifies the accumulated count the guest was spinning. > > > > > > So, it is increased when guest is spinning and reduced when spinlock is > > > released. > > > > But that's a global variable, so it might be incremented and decremented by > > several CPUs at once. I don't have the spec and have no time to study it > > either, but global does not make any sense to me. The spin wait info comes > > from a single guest CPU and the wakeup is targeted at that guest CPU as > > well. So why global? It might be defined that way, but then you really want > > to explain it proper. > > > > Thanks, > > > > tglx > > > Let me check this more. Will reply to you later. Thanks! > > BRs, > Yi Sun
I have got the details from Microsoft. Notify_Long_Spin_Wait hypercall should be called after a specific times spinning which can be got through CPUID. When hypervisor receives this, it will try to ensure that all vcpus are scheduled. Notify_Long_Spin_Wait is a standalone feature which should be split out as a new patch set. So I would like split it into a new patch set and submit it after PV Hyper-V Spinlock patch set merged.