There seems little point in disabling the FP/VMX/VSX MSR bits on context switch since we don't do it after calling enable_kernel_altivec() in other places. Writing the MSR is slow so lets not do it unnecessarily.
A context switch microbenchmark using yield(): http://ozlabs.org/~anton/junkcode/context_switch2.c ./context_switch2 --type=yield --fp 0 0 shows an improvement of almost 3% on POWER8. Signed-off-by: Anton Blanchard <an...@samba.org> --- arch/powerpc/kernel/entry_64.S | 15 +-------------- 1 file changed, 1 insertion(+), 14 deletions(-) diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index 579e0f9..daf00f5 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -441,26 +441,13 @@ _GLOBAL(_switch) SAVE_8GPRS(14, r1) SAVE_10GPRS(22, r1) mflr r20 /* Return to switch caller */ - mfmsr r22 - li r0, MSR_FP -#ifdef CONFIG_VSX -BEGIN_FTR_SECTION - oris r0,r0,MSR_VSX@h /* Disable VSX */ -END_FTR_SECTION_IFSET(CPU_FTR_VSX) -#endif /* CONFIG_VSX */ #ifdef CONFIG_ALTIVEC BEGIN_FTR_SECTION - oris r0,r0,MSR_VEC@h /* Disable altivec */ mfspr r24,SPRN_VRSAVE /* save vrsave register value */ std r24,THREAD_VRSAVE(r3) END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC) #endif /* CONFIG_ALTIVEC */ - and. r0,r0,r22 - beq+ 1f - andc r22,r22,r0 - MTMSRD(r22) - isync -1: std r20,_NIP(r1) + std r20,_NIP(r1) mfcr r23 std r23,_CCR(r1) std r1,KSP(r3) /* Set old stack pointer */ -- 2.1.4 _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
