From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [103.22.144.67]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4BB831A0133 for ; Sun, 26 Jul 2015 02:57:50 +1000 (AEST) From: Anton Blanchard To: benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, mikey@neuling.org, cyril.bur@au1.ibm.com Cc: linuxppc-dev@lists.ozlabs.org Subject: [PATCH 1/3] powerpc: No need to disable kernel FP/VMX/VSX MSR bits on context switch Date: Sun, 26 Jul 2015 02:57:43 +1000 Message-Id: <1437843465-1577-1-git-send-email-anton@samba.org> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 --- 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