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 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 C0661C433DB for ; Wed, 10 Feb 2021 02:00:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 729E564E56 for ; Wed, 10 Feb 2021 02:00:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235235AbhBJB7w (ORCPT ); Tue, 9 Feb 2021 20:59:52 -0500 Received: from kvm5.telegraphics.com.au ([98.124.60.144]:42958 "EHLO kvm5.telegraphics.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233717AbhBJA3c (ORCPT ); Tue, 9 Feb 2021 19:29:32 -0500 Received: from localhost (localhost.localdomain [127.0.0.1]) by kvm5.telegraphics.com.au (Postfix) with ESMTP id 677A622B35; Tue, 9 Feb 2021 19:28:33 -0500 (EST) Date: Wed, 10 Feb 2021 11:28:38 +1100 (AEDT) From: Finn Thain 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 In-Reply-To: <6712a7f16b99489db2828098dc3e03b2@hisilicon.com> Message-ID: <968b5f7a-5375-f0c6-c8c4-26ea6dabd9d1@telegraphics.com.au> References: <1612697823-8073-1-git-send-email-tanxiaofei@huawei.com> <31cd807d-3d0-ed64-60d-fde32cb3833c@telegraphics.com.au> <6712a7f16b99489db2828098dc3e03b2@hisilicon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? Moreover, there's no reason to believe that m68k is the only platform that supports nested interrupts. > > 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 >