[PATCH 25/32] sched: introduce the finish_arch_pre_lock_switch() scheduler hook

[David Carrillo-Cisneros <davidcc@google.com>]

This hook allows architecture specific code to be called at the end of
the task switch and after perf_events' context switch but before the
scheduler lock is released.

The specific use case in this series is to avoid multiple writes to a slow
MSR until all functions which modify such register in task switch have
finished.

Reviewed-by: Stephane Eranian <eranian@google.com>
Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
---
 arch/x86/include/asm/processor.h | 4 ++++
 kernel/sched/core.c              | 1 +
 kernel/sched/sched.h             | 3 +++
 3 files changed, 8 insertions(+)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 9264476..036d94a 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -22,6 +22,7 @@ struct vm86;
 #include <asm/nops.h>
 #include <asm/special_insns.h>
 #include <asm/fpu/types.h>
+#include <asm/pqr_common.h>
 
 #include <linux/personality.h>
 #include <linux/cache.h>
@@ -841,4 +842,7 @@ bool xen_set_default_idle(void);
 
 void stop_this_cpu(void *dummy);
 void df_debug(struct pt_regs *regs, long error_code);
+
+#define finish_arch_pre_lock_switch pqr_update
+
 #endif /* _ASM_X86_PROCESSOR_H */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8b489fc..bcd5473 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2620,6 +2620,7 @@ static struct rq *finish_task_switch(struct task_struct *prev)
 	prev_state = prev->state;
 	vtime_task_switch(prev);
 	perf_event_task_sched_in(prev, current);
+	finish_arch_pre_lock_switch();
 	finish_lock_switch(rq, prev);
 	finish_arch_post_lock_switch();
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ec2e8d2..cb48b5c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1077,6 +1077,9 @@ static inline int task_on_rq_migrating(struct task_struct *p)
 #ifndef prepare_arch_switch
 # define prepare_arch_switch(next)	do { } while (0)
 #endif
+#ifndef finish_arch_pre_lock_switch
+# define finish_arch_pre_lock_switch()	do { } while (0)
+#endif
 #ifndef finish_arch_post_lock_switch
 # define finish_arch_post_lock_switch()	do { } while (0)
 #endif
-- 
2.8.0.rc3.226.g39d4020