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 3vn0rY2B8gzDqZP for ; Tue, 21 Mar 2017 02:54:53 +1100 (AEDT) Received: from pps.filterd (m0098417.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v2KFrxgp115597 for ; Mon, 20 Mar 2017 11:54:41 -0400 Received: from e16.ny.us.ibm.com (e16.ny.us.ibm.com [129.33.205.206]) by mx0a-001b2d01.pphosted.com with ESMTP id 29aeabdyqb-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 20 Mar 2017 11:54:41 -0400 Received: from localhost by e16.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 20 Mar 2017 11:54:40 -0400 From: "Gautham R. Shenoy" To: Michael Ellerman , Michael Neuling , Benjamin Herrenschmidt , "Shreyas B. Prabhu" , Shilpasri G Bhat , Vaidyanathan Srinivasan , Anton Blanchard , Balbir Singh , Akshay Adiga , Nicholas Piggin Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, "Gautham R. Shenoy" Subject: [v2 PATCH 2/4] powernv:smp: Add busy-wait loop as fall back for CPU-Hotplug Date: Mon, 20 Mar 2017 21:24:16 +0530 In-Reply-To: References: In-Reply-To: References: Message-Id: <722d864e912cb0af6534b1ddef52ad3969ee9728.1490024477.git.ego@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: "Gautham R. Shenoy" Currently, the powernv cpu-offline function assumes that platform idle states such as stop on POWER9, winkle/sleep/nap on POWER8 are always available. On POWER8, it picks nap as the default state if other deep idle states like sleep/winkle are not available and enabled in the platform. On POWER9, nap is not available and all idle states are managed by STOP instruction. The parameters to the idle state are passed through processor stop status control register (PSSCR). Hence as such executing STOP would take parameters from current PSSCR. We do not want to make any assumptions in kernel on what STOP states and PSSCR features are configured by the platform. Ideally platform will configure a good set of stop states that can be used in the kernel. We would like to start with a clean slate, if the platform choose to not configure any state or there is an error in platform firmware that lead to no stop states being configured or allowed to be requested. This patch adds a fallback method for CPU-Hotplug that is similar to snooze loop at idle where the threads are left to spin at low priority and hence reduce the cycles consumed. This is a safe fallback mechanism in the case when no stop state would be requested if the platform firmware did not configure them most likely due to an error condition. Requesting a stop state when the platform has not configured them or enabled them would lead to further error conditions which could be difficult to debug. [Changelog written with inputs from svaidy@linux.vnet.ibm.com] Reviewed-by: Nicholas Piggin Signed-off-by: Gautham R. Shenoy --- arch/powerpc/platforms/powernv/idle.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c index 419edff..f335e0f 100644 --- a/arch/powerpc/platforms/powernv/idle.c +++ b/arch/powerpc/platforms/powernv/idle.c @@ -283,8 +283,16 @@ unsigned long pnv_cpu_offline(unsigned int cpu) } else if ((idle_states & OPAL_PM_SLEEP_ENABLED) || (idle_states & OPAL_PM_SLEEP_ENABLED_ER1)) { srr1 = power7_sleep(); - } else { + } else if (idle_states & OPAL_PM_NAP_ENABLED) { srr1 = power7_nap(1); + } else { + /* This is the fallback method. We emulate snooze */ + while (!generic_check_cpu_restart(cpu)) { + HMT_low(); + HMT_very_low(); + } + srr1 = 0; + HMT_medium(); } return srr1; -- 1.9.4