From: Heiko Carstens Date: Mon, 25 Oct 2010 14:10:18 +0000 (+0200) Subject: [S390] switch_to: dont restore/save access & fpu regs for kernel threads X-Git-Tag: v3.0~3030^2~36 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=fdb6d070effba1871f0bb980cf3c3b8738803414;p=platform%2Fkernel%2Flinux-amlogic.git [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 Signed-off-by: Martin Schwidefsky --- diff --git a/arch/s390/include/asm/system.h b/arch/s390/include/asm/system.h index 1f2ebc4..c35d0a3 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 *);