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

[Pan Xinhui]

Hi, Baibir
	sorry for late responce, I missed reading your mail.

å 16/7/6 18:54, Balbir Singh åé:
> On Tue, 2016-06-28 at 10:43 -0400, Pan Xinhui wrote:
> > 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
> 								^^ takes
> > 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
> 		   ^^ support
> > 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
> 					  ^^ yield
> > powerNV. So we can just skip the machine type.

Blame on me, I indeed need avoid such typo..
thanks for pointing it out.

> > Suggested-by: Boqun Feng <boqun.feng@xxxxxxxxx>
> > Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > Signed-off-by: Pan Xinhui <xinhui.pan@xxxxxxxxxxxxxxxxxx>
> > ---
> >  arch/powerpc/include/asm/spinlock.h | 18 ++++++++++++++++++
> >  1 file changed, 18 insertions(+)
> >
> > diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
> > index 523673d..3ac9fcb 100644
> > --- a/arch/powerpc/include/asm/spinlock.h
> > +++ b/arch/powerpc/include/asm/spinlock.h
> > @@ -52,6 +52,24 @@
> >  #define SYNC_IO
> >  #endif
> >
> > +/*
> > + * This support kernel to check if one cpu is preempted or not.
> > + * Then we can fix some lock holder preemption issue.
> > + */
> > +#ifdef CONFIG_PPC_PSERIES
> > +#define vcpu_is_preempted vcpu_is_preempted
> > +static inline bool vcpu_is_preempted(int cpu)
> > +{
> > +	/*
> > +	 * pSeries and powerNV can be built into same kernel image. In
> > +	 * principle we need return false directly if we are running as
> > +	 * powerNV. However the yield_count is always zero on powerNV, So
> > +	 * skip such machine type check
>
> Or you could use the ppc_md interface callbacks if required, but your
> solution works as well

thanks, So I can keep my code as is.

thanks
xinhui

> > +	 */
> > +	return !!(be32_to_cpu(lppaca_of(cpu).yield_count) & 1);
> > +}
> > +#endif
> > +
> >  static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
> >  {
> >  	return lock.slock == 0;
>
>
> Balbir Singh.