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=ham 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 180B6C18E01 for ; Tue, 20 Nov 2018 14:21:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8DC9F2087E for ; Tue, 20 Nov 2018 14:20:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8DC9F2087E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729651AbeKUAuE (ORCPT ); Tue, 20 Nov 2018 19:50:04 -0500 Received: from szxga07-in.huawei.com ([45.249.212.35]:41724 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726005AbeKUAuE (ORCPT ); Tue, 20 Nov 2018 19:50:04 -0500 Received: from DGGEMS404-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id 276697643F042; Tue, 20 Nov 2018 22:20:39 +0800 (CST) Received: from localhost.localdomain (10.175.124.28) by smtp.huawei.com (10.3.19.204) with Microsoft SMTP Server (TLS) id 14.3.408.0; Tue, 20 Nov 2018 22:20:32 +0800 From: Gao Xiang To: Greg Kroah-Hartman , CC: LKML , , "Chao Yu" , Miao Xie , , Gao Xiang Subject: [PATCH 03/10] staging: erofs: atomic_cond_read_relaxed on ref-locked workgroup Date: Tue, 20 Nov 2018 22:34:18 +0800 Message-ID: <20181120143425.43637-4-gaoxiang25@huawei.com> X-Mailer: git-send-email 2.14.4 In-Reply-To: <20181120143425.43637-1-gaoxiang25@huawei.com> References: <20181120143425.43637-1-gaoxiang25@huawei.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.175.124.28] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It's better to use atomic_cond_read_relaxed, which is implemented in hardware instructions to monitor a variable changes currently for ARM64, instead of open-coded busy waiting. Reviewed-by: Chao Yu Signed-off-by: Gao Xiang --- drivers/staging/erofs/internal.h | 30 ++++++++++++++++++------------ 1 file changed, 18 insertions(+), 12 deletions(-) diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h index 89dbd0888e53..eb80ba44d072 100644 --- a/drivers/staging/erofs/internal.h +++ b/drivers/staging/erofs/internal.h @@ -221,23 +221,29 @@ static inline void erofs_workgroup_unfreeze( preempt_enable(); } +#if defined(CONFIG_SMP) +static inline int erofs_wait_on_workgroup_freezed(struct erofs_workgroup *grp) +{ + return atomic_cond_read_relaxed(&grp->refcount, + VAL != EROFS_LOCKED_MAGIC); +} +#else +static inline int erofs_wait_on_workgroup_freezed(struct erofs_workgroup *grp) +{ + int v = atomic_read(&grp->refcount); + + /* workgroup is never freezed on uniprocessor systems */ + DBG_BUGON(v == EROFS_LOCKED_MAGIC); + return v; +} +#endif + static inline bool erofs_workgroup_get(struct erofs_workgroup *grp, int *ocnt) { - const int locked = (int)EROFS_LOCKED_MAGIC; int o; repeat: - o = atomic_read(&grp->refcount); - - /* spin if it is temporarily locked at the reclaim path */ - if (unlikely(o == locked)) { -#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK) - do - cpu_relax(); - while (atomic_read(&grp->refcount) == locked); -#endif - goto repeat; - } + o = erofs_wait_on_workgroup_freezed(grp); if (unlikely(o <= 0)) return -1; -- 2.14.4