Hi Xinhui,
On Mon, Sep 19, 2016 at 05:23:55AM -0400, Pan Xinhui wrote:
> Add two corresponding helper functions to support pv-qspinlock.
>
> For normal use, __spin_yield_cpu will confer current vcpu slices to the
> target vcpu(say, a lock holder). If target vcpu is not specified or it
> is in running state, such conferging to lpar happens or not depends.
>
> Because hcall itself will introduce latency and a little overhead. And
> we do NOT want to suffer any latency on some cases, e.g. in interrupt handler.
> The second parameter *confer* can indicate such case.
>
> __spin_wake_cpu is simpiler, it will wake up one vcpu regardless of its
> current vcpu state.
>
> Signed-off-by: Pan Xinhui <xinhui.pan@xxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/include/asm/spinlock.h | 4 +++
> arch/powerpc/lib/locks.c | 59 +++++++++++++++++++++++++++++++++++++
> 2 files changed, 63 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
> index 6aef8dd..abb6b0f 100644
> --- a/arch/powerpc/include/asm/spinlock.h
> +++ b/arch/powerpc/include/asm/spinlock.h
> @@ -56,9 +56,13 @@
> /* We only yield to the hypervisor if we are in shared processor mode */
> #define SHARED_PROCESSOR (lppaca_shared_proc(local_paca->lppaca_ptr))
> extern void __spin_yield(arch_spinlock_t *lock);
> +extern void __spin_yield_cpu(int cpu, int confer);
> +extern void __spin_wake_cpu(int cpu);
> extern void __rw_yield(arch_rwlock_t *lock);
> #else /* SPLPAR */
> #define __spin_yield(x) barrier()
> +#define __spin_yield_cpu(x,y) barrier()
> +#define __spin_wake_cpu(x) barrier()
> #define __rw_yield(x) barrier()
> #define SHARED_PROCESSOR 0
> #endif
> diff --git a/arch/powerpc/lib/locks.c b/arch/powerpc/lib/locks.c
> index 6574626..892df7d 100644
> --- a/arch/powerpc/lib/locks.c
> +++ b/arch/powerpc/lib/locks.c
> @@ -23,6 +23,65 @@
> #include <asm/hvcall.h>
> #include <asm/smp.h>
>
> +/*
> + * confer our slices to a specified cpu and return. If it is already running or
> + * cpu is -1, then we will check confer. If confer is NULL, we will return
> + * otherwise we confer our slices to lpar.
> + */
> +void __spin_yield_cpu(int cpu, int confer)
> +{
> + unsigned int holder_cpu = cpu, yield_count;
> +
You don't need @holder_cpu at all, do you?
> + if (cpu == -1)
> + goto yield_to_lpar;
> +
> + BUG_ON(holder_cpu >= nr_cpu_ids);
> + yield_count = be32_to_cpu(lppaca_of(holder_cpu).yield_count);
> +
> + /* if cpu is running, confer slices to lpar conditionally*/
> + if ((yield_count & 1) == 0)
> + goto yield_to_lpar;
> +
> + plpar_hcall_norets(H_CONFER,
> + get_hard_smp_processor_id(holder_cpu), yield_count);
> + return;
> +
> +yield_to_lpar:
> + if (confer)
> + plpar_hcall_norets(H_CONFER, -1, 0);
> +}
> +EXPORT_SYMBOL_GPL(__spin_yield_cpu);
> +
> +void __spin_wake_cpu(int cpu)
> +{
> + unsigned int holder_cpu = cpu;
> +
Ditto.
Regards,
Boqun
> + BUG_ON(holder_cpu >= nr_cpu_ids);
> + /*
> + * NOTE: we should always do this hcall regardless of
> + * the yield_count of the holder_cpu.
> + * as thers might be a case like below;
> + * CPU 1 2
> + * yielded = true
> + * if (yielded)
> + * __spin_wake_cpu()
> + * __spin_yield_cpu()
> + *
> + * So we might lose a wake if we check the yield_count and
> + * return directly if the holder_cpu is running.
> + * IOW. do NOT code like below.
> + * yield_count = be32_to_cpu(lppaca_of(holder_cpu).yield_count);
> + * if ((yield_count & 1) == 0)
> + * return;
> + *
> + * a PROD hcall marks the target_cpu proded, which cause the next cede or confer
> + * called on the target_cpu invalid.
> + */
> + plpar_hcall_norets(H_PROD,
> + get_hard_smp_processor_id(holder_cpu));
> +}
> +EXPORT_SYMBOL_GPL(__spin_wake_cpu);
> +
> #ifndef CONFIG_QUEUED_SPINLOCKS
> void __spin_yield(arch_spinlock_t *lock)
> {
> --
> 2.4.11
>
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