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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 8E3D2C433E0 for ; Thu, 25 Feb 2021 02:38:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5985864ED1 for ; Thu, 25 Feb 2021 02:38:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235202AbhBYCiP (ORCPT ); Wed, 24 Feb 2021 21:38:15 -0500 Received: from szxga04-in.huawei.com ([45.249.212.190]:12646 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234044AbhBYCiL (ORCPT ); Wed, 24 Feb 2021 21:38:11 -0500 Received: from DGGEMS404-HUB.china.huawei.com (unknown [172.30.72.58]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4DmH2v6nBLz16CR4; Thu, 25 Feb 2021 10:35:51 +0800 (CST) Received: from [127.0.0.1] (10.40.192.162) by DGGEMS404-HUB.china.huawei.com (10.3.19.204) with Microsoft SMTP Server id 14.3.498.0; Thu, 25 Feb 2021 10:37:26 +0800 Subject: Re: [Linuxarm] Re: [PATCH for-next 00/32] spin lock usage optimization for SCSI drivers To: Geert Uytterhoeven References: <1612697823-8073-1-git-send-email-tanxiaofei@huawei.com> CC: "James E.J. Bottomley" , "Martin K. Petersen" , scsi , "Linux Kernel Mailing List" , From: Xiaofei Tan Message-ID: <58053d07-ca58-2b78-36ff-40ecf162ed49@huawei.com> Date: Thu, 25 Feb 2021 10:37:26 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.40.192.162] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Geert, On 2021/2/24 17:41, Geert Uytterhoeven wrote: > Hi Xiaofei, > > On Sun, Feb 7, 2021 at 12:46 PM Xiaofei Tan wrote: >> Replace spin_lock_irqsave with spin_lock in hard IRQ of SCSI drivers. >> There are no function changes, but may speed up if interrupt happen >> too often. > > I'll bite: how much does this speed up interrupt processing? > What's the typical cost of saving/disabling, and restoring interrupt > state? It could only take a few CPU cycles. So there is little benefit for speeding up interrupt processing.You could take them as cleanup. Is removing this cost worth the risk of introducing subtle > regressions on platforms you cannot test yourself? > Currently, only found M68K platform support that high-priority interrupt preempts low-priority. No other platform has such services. Therefore, these changes do not affect non-M68K platforms. For M68K platform, no one report such interrupt preemption case in these SCSI drivers. > BTW, how many of these legacy SCSI controllers do you have access to? > Actually, no. > Thanks for your answers! > > Gr{oetje,eeting}s, > > Geert >