Re: [PATCH 2/3] powerpc/spinlock: support vcpu preempted check
From: Boqun Feng <hidden>
Date: 2016-06-27 14:55:29
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Hi Xinhui, On Mon, Jun 27, 2016 at 01:41:29PM -0400, Pan Xinhui wrote:
quoted hunk ↗ jump to hunk
This is to fix some holder preemption issues. Spinning at one vcpu which is preempted is meaningless. Kernel need such interfaces, So lets support it. We also should suooprt both the shared and dedicated mode. So add lppaca_dedicated_proc macro in lppaca.h Suggested-by: Boqun Feng <redacted> Signed-off-by: Pan Xinhui <redacted> --- arch/powerpc/include/asm/lppaca.h | 6 ++++++ arch/powerpc/include/asm/spinlock.h | 15 +++++++++++++++ 2 files changed, 21 insertions(+)diff --git a/arch/powerpc/include/asm/lppaca.h b/arch/powerpc/include/asm/lppaca.h index d0a2a2f..0a263d3 100644 --- a/arch/powerpc/include/asm/lppaca.h +++ b/arch/powerpc/include/asm/lppaca.h@@ -111,12 +111,18 @@ extern struct lppaca lppaca[]; * we will have to transition to something better. */ #define LPPACA_OLD_SHARED_PROC 2 +#define LPPACA_OLD_DEDICATED_PROC (1 << 6)
I think you should describe a little bit about the magic number here, i.e. what document/specification says this should work, and how this works.
quoted hunk ↗ jump to hunk
static inline bool lppaca_shared_proc(struct lppaca *l) { return !!(l->__old_status & LPPACA_OLD_SHARED_PROC); } +static inline bool lppaca_dedicated_proc(struct lppaca *l) +{ + return !!(l->__old_status & LPPACA_OLD_DEDICATED_PROC); +} + /* * SLB shadow buffer structure as defined in the PAPR. The save_area * contains adjacent ESID and VSID pairs for each shadowed SLB. Thediff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h index 523673d..ae938ee 100644 --- a/arch/powerpc/include/asm/spinlock.h +++ b/arch/powerpc/include/asm/spinlock.h@@ -52,6 +52,21 @@ #define SYNC_IO #endif +/* For fixing some spinning issues in a guest. + * kernel would check if vcpu is preempted during a spin loop. + * we support that. + */ +#define arch_vcpu_is_preempted arch_vcpu_is_preempted +static inline bool arch_vcpu_is_preempted(int cpu)
This function should be guarded by #ifdef PPC_PSERIES .. #endif, right? Because if the kernel is not compiled with guest support, vcpu_is_preempted() should always be false, right?
+{
+ struct lppaca *lp = &lppaca_of(cpu);
+
+ if (unlikely(!(lppaca_shared_proc(lp) ||
+ lppaca_dedicated_proc(lp))))Do you want to detect whether we are running in a guest(ie. pseries kernel) here? Then I wonder whether "machine_is(pseries)" works here. Regards, Boqun
+ return false;
+ return !!(be32_to_cpu(lp->yield_count) & 1);
+}
+
static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
{
return lock.slock == 0;
--
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