[PATCH v2 24/32] 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 right after
perf_events' context switch but before the scheduler lock is released.

It serves two uses in this patch series (introduced in next two patches):
  1) Calls CQM's cgroup context switch code that update the current RMID
  when no perf event is active (in continuous monitoring mode).
  2) Calls __pqr_ctx_switch to perform final write to the slow
  PQR_ASSOC msr in PQR's software.

Both use cases start monitoring for the next task, a role analogous to
that of perf_event_task_sched_in.

In future series, use case (1) will be expanded by Intel's CAT update to
the next CLOSID. Since Intel's CAT is independent to perf events, the hook
to perform (1) is not suitable to be in perf, yet, must be called as close
to perf sched_in as possible.

Reviewed-by: Stephane Eranian <eranian@google.com>
Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
---
 arch/x86/include/asm/processor.h | 1 +
 kernel/sched/core.c              | 1 +
 kernel/sched/sched.h             | 3 +++
 3 files changed, 5 insertions(+)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 9264476..c85fd82 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>
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d1f7149..a1200c2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2623,6 +2623,7 @@ 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