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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 F111EC433FF for ; Thu, 1 Aug 2019 12:17:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BDC1C216C8 for ; Thu, 1 Aug 2019 12:17:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="WGHtRa0y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730789AbfHAMRW (ORCPT ); Thu, 1 Aug 2019 08:17:22 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:50324 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726014AbfHAMRW (ORCPT ); Thu, 1 Aug 2019 08:17:22 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=dee5olqt7XlPjLLePVsNMyNo/Zg/J+KeegX7G29ctJE=; b=WGHtRa0yUM09pDDHuuiKDR7pv Pc3RFPJ1ikPHPGDtq379yWvLkjIGHBmehZWJjh1q2+0kKs/RxRzY+T0TOcGQRn8TXQ36H13My5gjU CaPk/hQEQwfast7p/7GOiTo11kk9mbEb0xuNk6FCVMaf96BURliBjRWb6BqUuv2CA+4KOprotj4Q1 SCchH46ixelfj0caeUsXRSqGp/MwebEFEmqXRhaxoY8ugFwCTQ9DwLYH2R5X9L1JKE+xfk1GE7mQo Reo+CvQJlxglqQP5ZtPVWT7j2pS2HVHOp6PqPm/FJ7p8Q3yTViiVKQJpXR/7851AamZGI0RFufw3W 5cpXbUERA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1htA1H-0007KB-VP; Thu, 01 Aug 2019 12:17:20 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 632452029F4C5; Thu, 1 Aug 2019 14:17:18 +0200 (CEST) Date: Thu, 1 Aug 2019 14:17:18 +0200 From: Peter Zijlstra To: Enric Balletbo i Serra Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, Benson Leung , Guenter Roeck , Mark Brown , linux-spi@vger.kernel.org, Doug Anderson Subject: Re: [PATCH 5/5] spi: Reduce kthread priority Message-ID: <20190801121718.GE31381@hirez.programming.kicks-ass.net> References: <20190801111348.530242235@infradead.org> <20190801111541.917256884@infradead.org> <640721f8-8a20-b161-473f-98a9dbc053cc@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <640721f8-8a20-b161-473f-98a9dbc053cc@collabora.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 01, 2019 at 01:27:04PM +0200, Enric Balletbo i Serra wrote: > > cc'ing Doug as he might be really interested on this patch > > On 1/8/19 13:13, Peter Zijlstra wrote: > > The SPI thingies request FIFO-99 by default, reduce this to FIFO-50. > > > > You say below that is not a suitable default but there is any other reason? Did > you observed problems with this? I didn't observe any problems with it personally. But imagine your device is used to control something critical, like something leathal, say a bandsaw. And just as you stick your hand through the laser guarding it, your SPI device chirps and preempts the task that was about to pull the emergency break and save your hand. FIFO-99 is the highest possible prio (for SCHED_FIFO) and by using it you say your task is the utmost imporant task on the system. I'm thinking that isn't true 99% of the time, except of course when that bandsaw emergency break is attached through SPI, but in that case the admin can very well chrt the prio of this thread.