From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3wfc4V667pzDqKX for ; Sat, 3 Jun 2017 06:58:18 +1000 (AEST) Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v52Krg3o026964 for ; Fri, 2 Jun 2017 16:58:09 -0400 Received: from e24smtp02.br.ibm.com (e24smtp02.br.ibm.com [32.104.18.86]) by mx0b-001b2d01.pphosted.com with ESMTP id 2au4r3bk4y-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 02 Jun 2017 16:58:09 -0400 Received: from localhost by e24smtp02.br.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 2 Jun 2017 17:58:07 -0300 Received: from d24av02.br.ibm.com (d24av02.br.ibm.com [9.8.31.93]) by d24relay04.br.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id v52KvvFA4129026 for ; Fri, 2 Jun 2017 17:58:05 -0300 Received: from d24av02.br.ibm.com (localhost [127.0.0.1]) by d24av02.br.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id v52KvXOZ030881 for ; Fri, 2 Jun 2017 17:57:33 -0300 From: Breno Leitao To: linuxppc-dev@lists.ozlabs.org Cc: Breno Leitao , Gustavo Romero Subject: [PATCH] powerpc/kernel: improve FP and vector registers restoration Date: Fri, 2 Jun 2017 17:56:43 -0300 Message-Id: <1496437003-32584-1-git-send-email-breno.leitao@gmail.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Currently tsk->thread->load_vec and load_fp are not initialized during a task creation, which set garbage to these variables (non-zero value). These variables will be checked later at restore_math() to validate if the FP and vectors are being utilized. Since these values might be non-zero, the restore_math() will continue to save the FP and vectors even if they were never utilized before the userspace application. load_fp and load_vec counters will then overflow and the FP and Altivec will be finally disabled, but before that condition is reached (counter overflow) several context switches restored FP and vector registers without need, causing a performance degradation. Signed-off-by: Breno Leitao Signed-off-by: Gustavo Romero --- arch/powerpc/kernel/process.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index baae104b16c7..a9435397eab8 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1666,6 +1666,7 @@ void start_thread(struct pt_regs *regs, unsigned long start, unsigned long sp) #ifdef CONFIG_VSX current->thread.used_vsr = 0; #endif + current->thread.load_fp = 0; memset(¤t->thread.fp_state, 0, sizeof(current->thread.fp_state)); current->thread.fp_save_area = NULL; #ifdef CONFIG_ALTIVEC @@ -1674,6 +1675,7 @@ void start_thread(struct pt_regs *regs, unsigned long start, unsigned long sp) current->thread.vr_save_area = NULL; current->thread.vrsave = 0; current->thread.used_vr = 0; + current->thread.load_vec = 0; #endif /* CONFIG_ALTIVEC */ #ifdef CONFIG_SPE memset(current->thread.evr, 0, sizeof(current->thread.evr)); -- 2.11.0