From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 84066C43387 for ; Thu, 3 Jan 2019 03:53:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5590821019 for ; Thu, 3 Jan 2019 03:53:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728628AbfACDx2 (ORCPT ); Wed, 2 Jan 2019 22:53:28 -0500 Received: from 59-120-53-16.HINET-IP.hinet.net ([59.120.53.16]:43485 "EHLO ATCSQR.andestech.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726136AbfACDx2 (ORCPT ); Wed, 2 Jan 2019 22:53:28 -0500 X-Greylist: delayed 1224 seconds by postgrey-1.27 at vger.kernel.org; Wed, 02 Jan 2019 22:53:27 EST Received: from ATCSQR.andestech.com (localhost [127.0.0.2] (may be forged)) by ATCSQR.andestech.com with ESMTP id x033al6P020432; Thu, 3 Jan 2019 11:36:47 +0800 (GMT-8) (envelope-from vincentc@andestech.com) Received: from mail.andestech.com (atcpcs16.andestech.com [10.0.1.222]) by ATCSQR.andestech.com with ESMTP id x033aQWw020403; Thu, 3 Jan 2019 11:36:26 +0800 (GMT-8) (envelope-from vincentc@andestech.com) Received: from atcsqa06.andestech.com (10.0.15.65) by ATCPCS16.andestech.com (10.0.1.222) with Microsoft SMTP Server id 14.3.123.3; Thu, 3 Jan 2019 11:32:40 +0800 From: Vincent Chen To: , , , , , CC: Vincent Chen Subject: [PATCH] RISC-V: Add _TIF_NEED_RESCHED check for kernel thread when CONFIG_PREEMPT=y Date: Thu, 3 Jan 2019 11:32:33 +0800 Message-ID: <1546486353-23115-1-git-send-email-vincentc@andestech.com> X-Mailer: git-send-email 2.7.4 MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.0.15.65] X-DNSRBL: X-MAIL: ATCSQR.andestech.com x033aQWw020403 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The cond_resched() can be used to yield the CPU resource if CONFIG_PREEMPT is not defined. Otherwise, cond_resched() is a dummy function. In order to avoid kernel thread occupying entire CPU, when CONFIG_PREEMPT=y, the kernel thread needs to follow the rescheduling mechanism like a user thread. Signed-off-by: Vincent Chen --- arch/riscv/kernel/asm-offsets.c | 1 + arch/riscv/kernel/entry.S | 18 +++++++++++++++++- 2 files changed, 18 insertions(+), 1 deletions(-) diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c index 6a92a2f..dac9834 100644 --- a/arch/riscv/kernel/asm-offsets.c +++ b/arch/riscv/kernel/asm-offsets.c @@ -39,6 +39,7 @@ void asm_offsets(void) OFFSET(TASK_STACK, task_struct, stack); OFFSET(TASK_TI, task_struct, thread_info); OFFSET(TASK_TI_FLAGS, task_struct, thread_info.flags); + OFFSET(TASK_TI_PREEMPT_COUNT, task_struct, thread_info.preempt_count); OFFSET(TASK_TI_KERNEL_SP, task_struct, thread_info.kernel_sp); OFFSET(TASK_TI_USER_SP, task_struct, thread_info.user_sp); OFFSET(TASK_TI_CPU, task_struct, thread_info.cpu); diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S index 13d4826..728b72d 100644 --- a/arch/riscv/kernel/entry.S +++ b/arch/riscv/kernel/entry.S @@ -144,6 +144,10 @@ _save_context: REG_L x2, PT_SP(sp) .endm +#if !IS_ENABLED(CONFIG_PREEMPT) +#define resume_kernel restore_all +#endif + ENTRY(handle_exception) SAVE_ALL @@ -228,7 +232,7 @@ ret_from_exception: REG_L s0, PT_SSTATUS(sp) csrc sstatus, SR_SIE andi s0, s0, SR_SPP - bnez s0, restore_all + bnez s0, resume_kernel resume_userspace: /* Interrupts must be disabled here so flags are checked atomically */ @@ -250,6 +254,18 @@ restore_all: RESTORE_ALL sret +#if IS_ENABLED(CONFIG_PREEMPT) +resume_kernel: + REG_L s0, TASK_TI_PREEMPT_COUNT(tp) + bnez s0, restore_all +need_resched: + REG_L s0, TASK_TI_FLAGS(tp) + andi s0, s0, _TIF_NEED_RESCHED + beqz s0, restore_all + call preempt_schedule_irq + j need_resched +#endif + work_pending: /* Enter slow path for supplementary processing */ la ra, ret_from_exception -- 1.7.1