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 5382AC433EF for ; Sat, 9 Apr 2022 02:17:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240571AbiDICTr (ORCPT ); Fri, 8 Apr 2022 22:19:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33162 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236449AbiDICTq (ORCPT ); Fri, 8 Apr 2022 22:19:46 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 01BD07E083; Fri, 8 Apr 2022 19:17:41 -0700 (PDT) Received: from kwepemi100015.china.huawei.com (unknown [172.30.72.55]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4KZzK01qTdzdZXM; Sat, 9 Apr 2022 10:17:08 +0800 (CST) Received: from kwepemm600009.china.huawei.com (7.193.23.164) by kwepemi100015.china.huawei.com (7.221.188.125) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Sat, 9 Apr 2022 10:17:38 +0800 Received: from [10.174.176.73] (10.174.176.73) by kwepemm600009.china.huawei.com (7.193.23.164) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.21; Sat, 9 Apr 2022 10:17:37 +0800 Subject: Re: [PATCH -next RFC v2 8/8] sbitmap: wake up the number of threads based on required tags To: Bart Van Assche , , , , CC: , , References: <20220408073916.1428590-1-yukuai3@huawei.com> <20220408073916.1428590-9-yukuai3@huawei.com> <6470d923-8fa5-cda1-e519-6f890cdcb00a@acm.org> From: "yukuai (C)" Message-ID: <4c322eee-3ad9-812f-a341-aa5e91573912@huawei.com> Date: Sat, 9 Apr 2022 10:17:37 +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: <6470d923-8fa5-cda1-e519-6f890cdcb00a@acm.org> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.176.73] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To kwepemm600009.china.huawei.com (7.193.23.164) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2022/04/09 5:13, Bart Van Assche 写道: > On 4/8/22 00:39, Yu Kuai wrote: >> +static unsigned int get_wake_nr(struct sbq_wait_state *ws, unsigned >> int nr_tags) >> +{ >> +    struct sbq_wait *wait; >> +    struct wait_queue_entry *entry; >> +    unsigned int nr = 1; >> + >> +    spin_lock_irq(&ws->wait.lock); >> +    list_for_each_entry(entry, &ws->wait.head, entry) { >> +        wait = container_of(entry, struct sbq_wait, wait); >> +        if (nr_tags <= wait->nr_tags) >> +            break; >> + >> +        nr++; >> +        nr_tags -= wait->nr_tags; >> +    } >> +    spin_unlock_irq(&ws->wait.lock); >> + >> +    return nr; >> +} >> + >>   static bool __sbq_wake_up(struct sbitmap_queue *sbq) >>   { >>       struct sbq_wait_state *ws; >> @@ -648,7 +668,7 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq) >>       smp_mb__before_atomic(); >>       atomic_set(&ws->wait_cnt, wake_batch); >>       sbq_update_preemption(sbq, wake_batch); >> -    wake_up_nr(&ws->wait, wake_batch); >> +    wake_up_nr(&ws->wait, get_wake_nr(ws, wake_batch)); >>       return true; >>   } > > An additional comment: my understanding is that __sbq_wake_up() should > wake up exactly `wake_batch` waiters. The above patch changes that into > waking up at most `wake_batch` waiters. I think that's wrong. Hi, I think the reason to wake up 'wake_batch' waiters is to make sure wakers will use up 'wake_batch' tags that is just freed, because each wakers should aquire at least one tag. Thus I think if we can make sure wakers will use up 'wake_batch' tags, it's ok to wake up less waiters. Please kindly correct me if I'm wrong. Thanks, Kuai > > Bart. > . >