From fdb6d070effba1871f0bb980cf3c3b8738803414 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <heiko.carstens@de.ibm.com>
Date: Mon, 25 Oct 2010 16:10:18 +0200
Subject: [PATCH] [S390] switch_to: dont restore/save access & fpu regs for
kernel threads
If the previous task was a kernel thread there is no need to save the
contents of the fpu and access registers since they aren't used in
kernel mode.
For the same reason it is not necessary to restore these registers if
the next task is a kernel thread.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
arch/s390/include/asm/system.h | 20 ++++++++++++--------
1 file changed, 12 insertions(+), 8 deletions(-)
diff --git a/arch/s390/include/asm/system.h b/arch/s390/include/asm/system.h
index 1f2ebc4afd82..c35d0a383f00 100644
--- a/arch/s390/include/asm/system.h
+++ b/arch/s390/include/asm/system.h
@@ -85,14 +85,18 @@ static inline void restore_access_regs(unsigned int *acrs)
asm volatile("lam 0,15,%0" : : "Q" (*acrs));
}
-#define switch_to(prev,next,last) do { \
- if (prev == next) \
- break; \
- save_fp_regs(&prev->thread.fp_regs); \
- restore_fp_regs(&next->thread.fp_regs); \
- save_access_regs(&prev->thread.acrs[0]); \
- restore_access_regs(&next->thread.acrs[0]); \
- prev = __switch_to(prev,next); \
+#define switch_to(prev,next,last) do { \
+ if (prev == next) \
+ break; \
+ if (prev->mm) { \
+ save_fp_regs(&prev->thread.fp_regs); \
+ save_access_regs(&prev->thread.acrs[0]); \
+ } \
+ if (next->mm) { \
+ restore_fp_regs(&next->thread.fp_regs); \
+ restore_access_regs(&next->thread.acrs[0]); \
+ } \
+ prev = __switch_to(prev,next); \
} while (0)
extern void account_vtime(struct task_struct *, struct task_struct *);
--
2.34.1