Christophe Leroy <christophe.le...@c-s.fr> writes: > By delaying the setting of MSR_RI, a 1% improvment is optained on > null_syscall selftest on an mpc8321. > > Without this patch: > > root@vgoippro:~# ./null_syscall > 1134.33 ns 378.11 cycles > > With this patch: > > root@vgoippro:~# ./null_syscall > 1121.85 ns 373.95 cycles > > The drawback is that a machine check during that period > would be unrecoverable, but as only main memory is accessed > during that period, it shouldn't be a concern.
On 64-bit server CPUs accessing main memory can cause a UE (Uncorrectable Error) which can trigger a machine check. So it may still be a concern, it depends how paranoid you are. > diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S > index 146385b1c2da..ea28a6ab56ec 100644 > --- a/arch/powerpc/kernel/head_32.S > +++ b/arch/powerpc/kernel/head_32.S > @@ -282,8 +282,6 @@ __secondary_hold_acknowledge: > stw r1,GPR1(r11); \ > stw r1,0(r11); \ > tovirt(r1,r11); /* set new kernel sp */ \ > - li r10,MSR_KERNEL & ~(MSR_IR|MSR_DR); /* can take exceptions */ \ > - MTMSRD(r10); /* (except for mach check in rtas) */ \ > stw r0,GPR0(r11); \ > lis r10,STACK_FRAME_REGS_MARKER@ha; /* exception frame marker */ \ > addi r10,r10,STACK_FRAME_REGS_MARKER@l; \ Where does RI get enabled? I don't see it anywhere obvious. cheers
