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Subject[patch 15/32] [PATCH] spinlock: check virtual cpu running status
From: Gerald Schaefer <gerald.schaefer@de.ibm.com>

This patch introduces a new function that checks the running status
of a cpu in a hypervisor. This status is not virtualized, so the check
is only correct if running in an LPAR. On acquiring a spinlock, if the
cpu holding the lock is scheduled by the hypervisor, we do a busy wait
on the lock. If it is not scheduled, we yield over to that cpu.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---

arch/s390/include/asm/sigp.h | 40 ++++++++++++++----------------
arch/s390/include/asm/smp.h | 24 ++++++++++++++++++
arch/s390/lib/spinlock.c | 57 +++++++++++++++++++++++++++++--------------
3 files changed, 82 insertions(+), 39 deletions(-)

Index: quilt-2.6/arch/s390/include/asm/sigp.h
===================================================================
--- quilt-2.6.orig/arch/s390/include/asm/sigp.h 2010-02-24 09:28:13.000000000 +0100
+++ quilt-2.6/arch/s390/include/asm/sigp.h 2010-02-24 09:44:25.000000000 +0100
@@ -31,32 +31,31 @@

typedef enum
{
- sigp_unassigned=0x0,
- sigp_sense,
- sigp_external_call,
- sigp_emergency_signal,
- sigp_start,
- sigp_stop,
- sigp_restart,
- sigp_unassigned1,
- sigp_unassigned2,
- sigp_stop_and_store_status,
- sigp_unassigned3,
- sigp_initial_cpu_reset,
- sigp_cpu_reset,
- sigp_set_prefix,
- sigp_store_status_at_address,
- sigp_store_extended_status_at_address
+ sigp_sense = 1,
+ sigp_external_call = 2,
+ sigp_emergency_signal = 3,
+ sigp_start = 4,
+ sigp_stop = 5,
+ sigp_restart = 6,
+ sigp_stop_and_store_status = 9,
+ sigp_initial_cpu_reset = 11,
+ sigp_cpu_reset = 12,
+ sigp_set_prefix = 13,
+ sigp_store_status_at_address = 14,
+ sigp_store_extended_status_at_address = 15,
+ sigp_set_architecture = 18,
+ sigp_conditional_emergency_signal = 19,
+ sigp_sense_running = 21,
} sigp_order_code;

typedef __u32 sigp_status_word;

typedef enum
{
- sigp_order_code_accepted=0,
- sigp_status_stored,
- sigp_busy,
- sigp_not_operational
+ sigp_order_code_accepted = 0,
+ sigp_status_stored = 1,
+ sigp_busy = 2,
+ sigp_not_operational = 3,
} sigp_ccode;


@@ -70,7 +69,6 @@
ec_schedule=0,
ec_call_function,
ec_call_function_single,
- ec_bit_last
} ec_bit_sig;

/*
Index: quilt-2.6/arch/s390/include/asm/smp.h
===================================================================
--- quilt-2.6.orig/arch/s390/include/asm/smp.h 2010-02-24 09:44:24.000000000 +0100
+++ quilt-2.6/arch/s390/include/asm/smp.h 2010-02-24 09:44:25.000000000 +0100
@@ -36,6 +36,28 @@
int from, int to);
extern void smp_restart_cpu(void);

+/*
+ * returns 1 if (virtual) cpu is scheduled
+ * returns 0 otherwise
+ */
+static inline int smp_vcpu_scheduled(int cpu)
+{
+ __u32 status = 0;
+
+ switch (signal_processor_ps(&status, 0, cpu, sigp_sense_running)) {
+ case sigp_status_stored:
+ /* Check for running status */
+ if (status & 0x400)
+ return 0;
+ break;
+ case sigp_not_operational:
+ return 0;
+ default:
+ break;
+ }
+ return 1;
+}
+
#else /* CONFIG_SMP */

static inline void smp_switch_to_ipl_cpu(void (*func)(void *), void *data)
@@ -43,6 +65,8 @@
func(data);
}

+#define smp_vcpu_scheduled (1)
+
#endif /* CONFIG_SMP */

#ifdef CONFIG_HOTPLUG_CPU
Index: quilt-2.6/arch/s390/lib/spinlock.c
===================================================================
--- quilt-2.6.orig/arch/s390/lib/spinlock.c 2010-02-24 09:28:13.000000000 +0100
+++ quilt-2.6/arch/s390/lib/spinlock.c 2010-02-24 09:44:25.000000000 +0100
@@ -43,16 +43,24 @@
{
int count = spin_retry;
unsigned int cpu = ~smp_processor_id();
+ unsigned int owner;

while (1) {
- if (count-- <= 0) {
- unsigned int owner = lp->owner_cpu;
- if (owner != 0)
- _raw_yield_cpu(~owner);
- count = spin_retry;
+ owner = lp->owner_cpu;
+ if (!owner || smp_vcpu_scheduled(~owner)) {
+ for (count = spin_retry; count > 0; count--) {
+ if (arch_spin_is_locked(lp))
+ continue;
+ if (_raw_compare_and_swap(&lp->owner_cpu, 0,
+ cpu) == 0)
+ return;
+ }
+ if (MACHINE_IS_LPAR)
+ continue;
}
- if (arch_spin_is_locked(lp))
- continue;
+ owner = lp->owner_cpu;
+ if (owner)
+ _raw_yield_cpu(~owner);
if (_raw_compare_and_swap(&lp->owner_cpu, 0, cpu) == 0)
return;
}
@@ -63,17 +71,27 @@
{
int count = spin_retry;
unsigned int cpu = ~smp_processor_id();
+ unsigned int owner;

local_irq_restore(flags);
while (1) {
- if (count-- <= 0) {
- unsigned int owner = lp->owner_cpu;
- if (owner != 0)
- _raw_yield_cpu(~owner);
- count = spin_retry;
+ owner = lp->owner_cpu;
+ if (!owner || smp_vcpu_scheduled(~owner)) {
+ for (count = spin_retry; count > 0; count--) {
+ if (arch_spin_is_locked(lp))
+ continue;
+ local_irq_disable();
+ if (_raw_compare_and_swap(&lp->owner_cpu, 0,
+ cpu) == 0)
+ return;
+ local_irq_restore(flags);
+ }
+ if (MACHINE_IS_LPAR)
+ continue;
}
- if (arch_spin_is_locked(lp))
- continue;
+ owner = lp->owner_cpu;
+ if (owner)
+ _raw_yield_cpu(~owner);
local_irq_disable();
if (_raw_compare_and_swap(&lp->owner_cpu, 0, cpu) == 0)
return;
@@ -100,8 +118,11 @@
void arch_spin_relax(arch_spinlock_t *lock)
{
unsigned int cpu = lock->owner_cpu;
- if (cpu != 0)
- _raw_yield_cpu(~cpu);
+ if (cpu != 0) {
+ if (MACHINE_IS_VM || MACHINE_IS_KVM ||
+ !smp_vcpu_scheduled(~cpu))
+ _raw_yield_cpu(~cpu);
+ }
}
EXPORT_SYMBOL(arch_spin_relax);



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