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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 DAD38C433DB for ; Wed, 10 Feb 2021 00:40:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A2ADB64E4F for ; Wed, 10 Feb 2021 00:40:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234487AbhBJAkP convert rfc822-to-8bit (ORCPT ); Tue, 9 Feb 2021 19:40:15 -0500 Received: from szxga02-in.huawei.com ([45.249.212.188]:3436 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234457AbhBJAiX (ORCPT ); Tue, 9 Feb 2021 19:38:23 -0500 Received: from DGGEMM404-HUB.china.huawei.com (unknown [172.30.72.56]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4Db15l4btWz5Qwd; Wed, 10 Feb 2021 08:36:11 +0800 (CST) Received: from dggemi761-chm.china.huawei.com (10.1.198.147) by DGGEMM404-HUB.china.huawei.com (10.3.20.212) with Microsoft SMTP Server (TLS) id 14.3.498.0; Wed, 10 Feb 2021 08:37:35 +0800 Received: from dggemi761-chm.china.huawei.com (10.1.198.147) by dggemi761-chm.china.huawei.com (10.1.198.147) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2106.2; Wed, 10 Feb 2021 08:37:35 +0800 Received: from dggemi761-chm.china.huawei.com ([10.9.49.202]) by dggemi761-chm.china.huawei.com ([10.9.49.202]) with mapi id 15.01.2106.006; Wed, 10 Feb 2021 08:37:35 +0800 From: "Song Bao Hua (Barry Song)" To: Finn Thain CC: tanxiaofei , "jejb@linux.ibm.com" , "martin.petersen@oracle.com" , "linux-scsi@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linuxarm@openeuler.org" , "linux-m68k@vger.kernel.org" Subject: RE: [Linuxarm] Re: [PATCH for-next 00/32] spin lock usage optimization for SCSI drivers Thread-Topic: [Linuxarm] Re: [PATCH for-next 00/32] spin lock usage optimization for SCSI drivers Thread-Index: AQHW/fAMrBMz1ua2YUiLJwcWnjqnW6pPDROA//+zewCAAIlDYIAAu4wAgACFBAA= Date: Wed, 10 Feb 2021 00:37:34 +0000 Message-ID: <4ee3b4fa65ee4773aa520c192b262dbb@hisilicon.com> References: <1612697823-8073-1-git-send-email-tanxiaofei@huawei.com> <31cd807d-3d0-ed64-60d-fde32cb3833c@telegraphics.com.au> <6712a7f16b99489db2828098dc3e03b2@hisilicon.com> <968b5f7a-5375-f0c6-c8c4-26ea6dabd9d1@telegraphics.com.au> In-Reply-To: <968b5f7a-5375-f0c6-c8c4-26ea6dabd9d1@telegraphics.com.au> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.126.202.77] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org > -----Original Message----- > From: Finn Thain [mailto:fthain@telegraphics.com.au] > Sent: Wednesday, February 10, 2021 1:29 PM > To: Song Bao Hua (Barry Song) > Cc: tanxiaofei ; jejb@linux.ibm.com; > martin.petersen@oracle.com; linux-scsi@vger.kernel.org; > linux-kernel@vger.kernel.org; linuxarm@openeuler.org; > linux-m68k@vger.kernel.org > Subject: RE: [Linuxarm] Re: [PATCH for-next 00/32] spin lock usage optimization > for SCSI drivers > > On Tue, 9 Feb 2021, Song Bao Hua (Barry Song) wrote: > > > > On Tue, 9 Feb 2021, Song Bao Hua (Barry Song) wrote: > > > > > > > > On Sun, 7 Feb 2021, 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. > > > > > > > > > > This change doesn't necessarily work on platforms that support > > > > > nested interrupts. > > > > > > > > > > Were you able to measure any benefit from this change on some > > > > > other platform? > > > > > > > > I think the code disabling irq in hardIRQ is simply wrong. Since > > > > this commit > > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/ > ?id=e58aa3d2d0cc > > > > genirq: Run irq handlers with interrupts disabled > > > > > > > > interrupt handlers are definitely running in a irq-disabled context > > > > unless irq handlers enable them explicitly in the handler to permit > > > > other interrupts. > > > > > > > > > > Repeating the same claim does not somehow make it true. > > > > Sorry for I didn't realize xiaofei had replied. > > > > I was referring to the claim in patch 00/32, i.e. that interrupt handlers > only run when irqs are disabled. > > > > If you put your claim to the test, you'll see that that interrupts are > > > not disabled on m68k when interrupt handlers execute. > > > > Sounds like an implementation issue of m68k since IRQF_DISABLED has been > > totally removed. > > > > It's true that IRQF_DISABLED could be used to avoid the need for irq locks > in interrupt handlers. So, if you want to remove irq locks from interrupt > handlers, today you can't use IRQF_DISABLED to help you. So what? > > > > > > > The Interrupt Priority Level (IPL) can prevent any given irq handler > > > from being re-entered, but an irq with a higher priority level may be > > > handled during execution of a lower priority irq handler. > > > > > > > We used to have IRQF_DISABLED to support so-called "fast interrupt" to > > avoid this. > > > > But the concept has been totally removed. That is interesting if m68k > > still has this issue. > > > > Prioritized interrupts are beneficial. Why would you want to avoid them? > I doubt this is true as it has been already thought as unnecessary in Linux: https://lwn.net/Articles/380931/ > Moreover, there's no reason to believe that m68k is the only platform that > supports nested interrupts. I doubt that is true as genirq is running understand the consumption that hardIRQ is running in irq-disabled context: "We run all handlers with interrupts disabled and expect them not to enable them. Warn when we catch one who does." https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b738a50a If it is, m68k is against the assumption of genirq. > > > > sonic_interrupt() uses an irq lock within an interrupt handler to > > > avoid issues relating to this. This kind of locking may be needed in > > > the drivers you are trying to patch. Or it might not. Apparently, > > > no-one has looked. > > Thanks Barry