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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 665E4ECAAD5 for ; Fri, 2 Sep 2022 10:02:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235746AbiIBKCW (ORCPT ); Fri, 2 Sep 2022 06:02:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51758 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234162AbiIBKCM (ORCPT ); Fri, 2 Sep 2022 06:02:12 -0400 Received: from dggsgout12.his.huawei.com (dggsgout12.his.huawei.com [45.249.212.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2C5679A9AD; Fri, 2 Sep 2022 03:02:09 -0700 (PDT) Received: from mail02.huawei.com (unknown [172.30.67.143]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTP id 4MJth93Yyjz6S93D; Fri, 2 Sep 2022 18:00:25 +0800 (CST) Received: from [10.174.176.73] (unknown [10.174.176.73]) by APP2 (Coremail) with SMTP id Syh0CgDHGXOe1BFjcdgPAQ--.13112S3; Fri, 02 Sep 2022 18:02:07 +0800 (CST) Subject: Re: [PATCH -next 2/3] md/raid10: convert resync_lock to use seqlock To: Guoqing Jiang , Yu Kuai , song@kernel.org Cc: linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, yi.zhang@huawei.com, "yukuai (C)" References: <20220829131502.165356-1-yukuai1@huaweicloud.com> <20220829131502.165356-3-yukuai1@huaweicloud.com> <3d8859bc-80d6-08b0-fd40-8874df4d3419@linux.dev> From: Yu Kuai Message-ID: <1891ec2c-0ccc-681e-31de-fdd28eebce82@huaweicloud.com> Date: Fri, 2 Sep 2022 18:02:05 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <3d8859bc-80d6-08b0-fd40-8874df4d3419@linux.dev> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID: Syh0CgDHGXOe1BFjcdgPAQ--.13112S3 X-Coremail-Antispam: 1UD129KBjvdXoWrKF48Xw47Gw13Wr4fKw1xXwb_yoWfuwc_K3 98Wr1DWFW5J3y7Kr1qgr42vr9rtr1jkr1jyan0yF15G3W5GFZ8Jr1rXa95Jr15Gr45Jrnx uryfua43t3WUujkaLaAFLSUrUUUUUb8apTn2vfkv8UJUUUU8Yxn0WfASr-VFAUDa7-sFnT 9fnUUIcSsGvfJTRUUUb4kFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k26cxKx2IYs7xG 6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4vEj48ve4kI8w A2z4x0Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7CjxVAFwI0_Gr1j 6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x0267AKxVW0oV Cq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0 I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r 4UM4x0Y48IcVAKI48JM4x0x7Aq67IIx4CEVc8vx2IErcIFxwCYjI0SjxkI62AI1cAE67vI Y487MxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8CrVAFwI 0_Jr0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUAVWUtwCIc40Y 0x0EwIxGrwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x0267AKxV WUJVW8JwCI42IY6xAIw20EY4v20xvaj40_WFyUJVCq3wCI42IY6I8E87Iv67AKxVWUJVW8 JwCI42IY6I8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjfUoOJ5UU UUU X-CM-SenderInfo: 51xn3trlr6x35dzhxuhorxvhhfrp/ X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org Hi, 在 2022/09/02 17:42, Guoqing Jiang 写道: > Hi, > > On 8/29/22 9:15 PM, Yu Kuai wrote: >> +static bool wait_barrier_nolock(struct r10conf *conf) >> +{ >> +    unsigned int seq = raw_read_seqcount(&conf->resync_lock.seqcount); >> + >> +    if (seq & 1) >> +        return false; >> + >> +    if (READ_ONCE(conf->barrier)) >> +        return false; >> + >> +    atomic_inc(&conf->nr_pending); >> +    if (!read_seqcount_retry(&conf->resync_lock.seqcount, seq)) > > I think 'seq' is usually get from read_seqcount_begin. read_seqcount_begin will loop untill "req & 1" failed, I'm afraid this will cause high cpu usage in come cases. What I try to do here is just try once, and fall back to hold lock and wait if failed. What do you think? Thanks, Kuai > >> +        return true; >> + >> +    atomic_dec(&conf->nr_pending); >> +    return false; >> + > > Thanks, > Guoqing > . >