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 5CCFDC77B7A for ; Tue, 30 May 2023 02:19:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230070AbjE3CT4 (ORCPT ); Mon, 29 May 2023 22:19:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56212 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229489AbjE3CTy (ORCPT ); Mon, 29 May 2023 22:19:54 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6553DDB for ; Mon, 29 May 2023 19:19:53 -0700 (PDT) Received: from kwepemi500012.china.huawei.com (unknown [172.30.72.53]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4QVb7F0CGsz18Lkn; Tue, 30 May 2023 09:54:49 +0800 (CST) Received: from [10.67.110.108] (10.67.110.108) by kwepemi500012.china.huawei.com (7.221.188.12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.23; Tue, 30 May 2023 09:59:25 +0800 Message-ID: <56c6dc9a-a5a6-368a-abd4-cace43ceaec0@huawei.com> Date: Tue, 30 May 2023 09:59:24 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH v5 1/3] genirq: Use hlist for managing resend handlers To: Thomas Gleixner , Shanker Donthineni , Marc Zyngier CC: Sebastian Andrzej Siewior , Michael Walle , , Vikram Sethi , Jason Sequeira References: <20230519134902.1495562-1-sdonthineni@nvidia.com> <20230519134902.1495562-2-sdonthineni@nvidia.com> <6dc6642a-1e7c-f111-1fa2-be54826ecef6@huawei.com> <871qiylsc9.ffs@tglx> From: "Liao, Chang" In-Reply-To: <871qiylsc9.ffs@tglx> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.110.108] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemi500012.china.huawei.com (7.221.188.12) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Thomas 在 2023/5/30 5:51, Thomas Gleixner 写道: > On Mon, May 29 2023 at 15:57, Chang Liao wrote: >> 在 2023/5/19 21:49, Shanker Donthineni 写道: >>> diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h >>> index 844a8e30e6de..d9451d456a73 100644 >>> --- a/include/linux/irqdesc.h >>> +++ b/include/linux/irqdesc.h >>> @@ -102,6 +102,9 @@ struct irq_desc { >>> int parent_irq; >>> struct module *owner; >>> const char *name; >>> +#ifdef CONFIG_HARDIRQS_SW_RESEND >>> + struct hlist_node resend_node; >>> +#endif >>> } ____cacheline_internodealigned_in_smp; >> >> Although there is no documented rule that limits the change of the KABI >> struct irq_desc, it is still better to keep the irq_desc definition >> stable. > > Please read and understand: > > Documentation/process/stable-api-nonsense.rst > > If you want KABI, then that's _YOUR_ problem, period. Thanks for the guide. > >>> -/* Bitmap to handle software resend of interrupts: */ >>> -static DECLARE_BITMAP(irqs_resend, IRQ_BITMAP_BITS); >>> +/* hlist_head to handle software resend of interrupts: */ >>> +static HLIST_HEAD(irq_resend_list); >>> +static DEFINE_RAW_SPINLOCK(irq_resend_lock); >> >> What is the benefit of using hlist here? If you want to enjoy the >> low latency of querying elements by key, you must define a hlist table >> with a reasonable number of buckets. Otherwise, I don't think the time >> complexity of hlist is better than a regular double-linked list, >> right? > > What's complex about hlist in this case? Please explain. Honestly, it is not about the complexity. Perhaps I do not understand the usage of hlist very deeply. I have searched some codes in the kernel and found that hlist is always used to speed up arbitrary querying, such as searching a registered kprobe by address. Back to this patch, these resend IRQs are organized in a sequence list actually, and traveled one by one to handle. Further, by comparing the difference between hlist_empty, hlist_add_head, hlist_del_init, and their counterparts in list, it looks like a regular linked list is also good enough. Thanks. > > Thanks, > > tglx -- BR Liao, Chang