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 87963CD493F for ; Thu, 21 Sep 2023 02:12:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229817AbjIUCMh (ORCPT ); Wed, 20 Sep 2023 22:12:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40088 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229730AbjIUCMe (ORCPT ); Wed, 20 Sep 2023 22:12:34 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2DA23CF for ; Wed, 20 Sep 2023 19:12:29 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1695262347; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zGsXb59mheAvf0K/E0GO3/Bp/8mZXCu36PHW8K2vlxI=; b=4aQW4w2uUjAKLLA6iOdyat5+SCt1rP/XPruRshfBLZMyyz/uU/1fO/sKn0Irl5vexExvji zJJnqqH3YsCaEuZqb+q4bEntoeYsp1xYDng9TUXHuMJgMTMfwFRQYr0orDJoR/wOxaSCxQ AoDXS9VVwYTCAVBkgzHC0oscSF1EkN3gTvrI4IJ5spFelSSCtqKBiE5aHioWUV3rbdsMim G8Hx+AX1upPFu9TC+vKCdRnyGBt1uygWDZWvmXuu3U+Sw6gdkfvXBk9/i/hKEXRqaJwwRL rQsdgaoFwC32fuD3aCS+8tMgnfJoOEeDaciNMMoH451sm8mhVNiwwuxsXfiCyA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1695262347; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zGsXb59mheAvf0K/E0GO3/Bp/8mZXCu36PHW8K2vlxI=; b=sO/9/fISUk77aPbQ2sgJ2s84yiEHYYsGdaG620hmsx1tZu4FTAjI7ObUu0kwFasGSwfcVv 212YTsmnxSsObHAg== To: Ankur Arora Cc: Linus Torvalds , Peter Zijlstra , Ankur Arora , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, rostedt@goodmis.org, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, jgross@suse.com, andrew.cooper3@citrix.com Subject: Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED In-Reply-To: <875y44ibow.fsf@oracle.com> References: <20230830184958.2333078-8-ankur.a.arora@oracle.com> <20230908070258.GA19320@noisy.programming.kicks-ass.net> <87zg1v3xxh.fsf@oracle.com> <87edj64rj1.fsf@oracle.com> <87zg1u1h5t.fsf@oracle.com> <20230911150410.GC9098@noisy.programming.kicks-ass.net> <87h6o01w1a.fsf@oracle.com> <20230912082606.GB35261@noisy.programming.kicks-ass.net> <87cyyfxd4k.ffs@tglx> <87led2wdj0.ffs@tglx> <878r90lyai.fsf@oracle.com> <875y44va9t.ffs@tglx> <875y44ibow.fsf@oracle.com> Date: Thu, 21 Sep 2023 04:12:27 +0200 Message-ID: <87r0mstgtw.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 20 2023 at 17:58, Ankur Arora wrote: > Thomas Gleixner writes: >> So no, we don't need yet another knob. We keep them chucking along and >> if they really want they can adopt to the new world order. :) > > Will they chuckle along, or die trying ;)? Either way is fine :) > I grepped for "preempt_enable|preempt_disable" for all the archs and > hexagon and m68k don't seem to do any explicit accounting at all. > (Though, neither do nios2 and openrisc, and both csky and microblaze > only do it in the tlbflush path.) > > arch/hexagon 0 > arch/m68k 0 ... > arch/s390 91 > arch/mips 115 > arch/x86 146 > arch/powerpc 201 > > My concern is given that we preempt on timeslice expiration for all > three preemption models, we could end up preempting at an unsafe > location. As I said in my reply to Linus, that count is not really conclusive. arch/m68k has a count of 0 and supports PREEMPT for the COLDFIRE sub-architecture and I know for sure that at some point in the past PREEMPT_RT was supported on COLDFIRE with minimal changes to the architecture code. That said, I'm pretty sure that quite some of these preempt_disable/enable pairs in arch/* are subject to voodoo programming, but that's a different problem to analyze. > Still, not the most pressing of problems. Exactly :) Thanks, tglx