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Date: Wed, 06 Jul 2016 20:54:14 +1000 From: Balbir Singh <bsingharora@...il.com> To: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, virtualization@...ts.linux-foundation.org, linux-s390@...r.kernel.org Cc: dave@...olabs.net, peterz@...radead.org, mpe@...erman.id.au, boqun.feng@...il.com, will.deacon@....com, waiman.long@....com, mingo@...hat.com, paulus@...ba.org, benh@...nel.crashing.org, schwidefsky@...ibm.com, paulmck@...ux.vnet.ibm.com Subject: Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check 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. > > Suggested-by: Boqun Feng <boqun.feng@...il.com> > Suggested-by: Peter Zijlstra (Intel) <peterz@...radead.org> > Signed-off-by: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com> > --- > 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 > + */ > + 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.
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