[PATCHv2 3/3] processor: get rid of cpu_relax_yield

Heiko Carstens
2019-06-13T10:35:22Z

stop_machine is the only user left of cpu_relax_yield. Given that it
now has special semantics which are tied to stop_machine introduce a
weak stop_machine_yield function which architectures can override, and
get rid of the generic cpu_relax_yield implementation.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
---
arch/s390/include/asm/processor.h | 6 ------
arch/s390/kernel/processor.c | 4 ++--
include/linux/sched.h | 4 ----
include/linux/stop_machine.h | 1 +
kernel/stop_machine.c | 7 ++++++-
5 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index 445ce9ee4404..14883b1562e0 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -222,12 +222,6 @@ static __no_kasan_or_inline unsigned short stap(void)
return cpu_address;
}

-/*
- * Give up the time slice of the virtual PU.
- */
-#define cpu_relax_yield cpu_relax_yield
-void cpu_relax_yield(const struct cpumask *cpumask);
-
#define cpu_relax() barrier()

#define ECAG_CACHE_ATTRIBUTE 0
diff --git a/arch/s390/kernel/processor.c b/arch/s390/kernel/processor.c
index 4cdaefec1b7c..6ebc2117c66c 100644
--- a/arch/s390/kernel/processor.c
+++ b/arch/s390/kernel/processor.c
@@ -7,6 +7,7 @@
#define KMSG_COMPONENT "cpu"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

+#include <linux/stop_machine.h>
#include <linux/cpufeature.h>
#include <linux/bitops.h>
#include <linux/kernel.h>
@@ -59,7 +60,7 @@ void s390_update_cpu_mhz(void)
on_each_cpu(update_cpu_mhz, NULL, 0);
}

-void notrace cpu_relax_yield(const struct cpumask *cpumask)
+void notrace stop_machine_yield(const struct cpumask *cpumask)
{
int cpu, this_cpu;

@@ -73,7 +74,6 @@ void notrace cpu_relax_yield(const struct cpumask *cpumask)
smp_yield_cpu(cpu);
}
}
-EXPORT_SYMBOL(cpu_relax_yield);

/*
* cpu_init - initializes state that is per-CPU.
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1f9f3160da7e..911675416b05 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1518,10 +1518,6 @@ static inline int set_cpus_allowed_ptr(struct task_struct *p, const struct cpuma
}
#endif

-#ifndef cpu_relax_yield
-#define cpu_relax_yield(cpumask) cpu_relax()
-#endif
-
extern int yield_to(struct task_struct *p, bool preempt);
extern void set_user_nice(struct task_struct *p, long nice);
extern int task_prio(const struct task_struct *p);
diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h
index 6d3635c86dbe..f9a0c6189852 100644
--- a/include/linux/stop_machine.h
+++ b/include/linux/stop_machine.h
@@ -36,6 +36,7 @@ int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg);
int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg);
void stop_machine_park(int cpu);
void stop_machine_unpark(int cpu);
+void stop_machine_yield(const struct cpumask *cpumask);

#else /* CONFIG_SMP */

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index b8b0c5ff8da9..b4f83f7bdf86 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -177,6 +177,11 @@ static void ack_state(struct multi_stop_data *msdata)
set_state(msdata, msdata->state + 1);
}

+void __weak stop_machine_yield(const struct cpumask *cpumask)
+{
+ cpu_relax();
+}
+
/* This is the cpu_stop function which stops the CPU. */
static int multi_cpu_stop(void *data)
{
@@ -204,7 +209,7 @@ static int multi_cpu_stop(void *data)
/* Simple state machine */
do {
/* Chill out and ensure we re-read multi_stop_state. */
- cpu_relax_yield(cpumask);
+ stop_machine_yield(cpumask);
if (msdata->state != curstate) {
curstate = msdata->state;
switch (curstate) {
--
2.17.1