From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F087F1DDC06 for ; Tue, 8 Oct 2024 14:40:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728398419; cv=none; b=OePRUhQqm5Js55968nAiuAtmIGT11FWDNKxk2E6yZeDUPXiQmh75NiylRUeQzGo3P+jPRG9rjMHNSbQcPO8Fx2HO0vz3UcSREtQj2AnUu4BK1dL0RhwoBhztYr+UoO1kEC/hOJDjrCBJYOnkj5y9dWp5nqHDF+AM/tQF1wlU7mI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728398419; c=relaxed/simple; bh=KSa+Htif7D8W1ofiVoyQYbozJ7rBbB491hmGrraEtv0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=e9GCIuBYdt/Qh2OSrzUKvl4xKuwhqX9cusHkPlER1j8HS7z3uJpwmkOcbPepwmOjyB2oH6Bm0hX+MeJj365s7dVHsV9O048A+4xWIMXYNIHruGRBbj7Wz6mDqlrGUqE06cXm1pRaNKims9ldA8Nxz/X8lckTj5/7lyO6fAW0q/c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=GVWSGBvi; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="GVWSGBvi" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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; bh=IRk7aB98URQob2gIEwpN+sXWoMo/G4yD2aImdLcMbBc=; b=GVWSGBviHvlAOhGVvqaMgbZy+i HqDvHgoc/AamYg12BHmE3eld9uOvYfE0UVax2HqaUlomGUkDhBe+7qMTcSOuceVl3N1aFJOh8sdGO m+6e5NRRVLICOZnHwY/4o5aCS6N0HOcCdZCPpYhDqlOKoolmUv++SA8WN0GxkMbu+K2NM2aXh3SES DQVdQXoAD3QA3ufHWXbWWFSuNfRCMoEDmp4VPNStkG7etfpqONa5Awxxkcf0u8CKsiy5ZjM/JBHFA Uo34E1JEalSfUF3lOxmgp/2G6YFX+zenQ2eBl5/bQ9MtUVEDgQiiW3magnGbo/L0UkXht0e7Df5Xq QNz5t9Xw==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1syBNa-00000004dKz-2ulS; Tue, 08 Oct 2024 14:40:02 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id E1284300599; Tue, 8 Oct 2024 16:40:00 +0200 (CEST) Date: Tue, 8 Oct 2024 16:40:00 +0200 From: Peter Zijlstra To: Sebastian Andrzej Siewior Cc: tglx@linutronix.de, mingo@kernel.org, linux-kernel@vger.kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, ankur.a.arora@oracle.com, efault@gmx.de, Clark Williams Subject: Re: [PATCH 3/5] sched: Enable PREEMPT_DYNAMIC for PREEMPT_RT Message-ID: <20241008144000.GE14587@noisy.programming.kicks-ass.net> References: <20241007074609.447006177@infradead.org> <20241007075055.441622332@infradead.org> <20241008132416.9cVldCGG@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241008132416.9cVldCGG@linutronix.de> On Tue, Oct 08, 2024 at 03:24:16PM +0200, Sebastian Andrzej Siewior wrote: > On 2024-10-07 09:46:12 [+0200], Peter Zijlstra wrote: > > In order to enable PREEMPT_DYNAMIC for PREEMPT_RT, remove PREEMPT_RT > > from the 'Preemption Model' choice. Strictly speaking PREEMPT_RT is > > not a change in how preemption works, but rather it makes a ton more > > code preemptible. > > > > Notably, take away NONE and VOLATILE options for PREEMPT_RT, they make As I think Mike already noted, typing is hard and this should of course have been Voluntary :-) > > no sense (but are techincally possible). > > So this is what we do. Okay. This means we can enable the DYNAMIC mode > on PREEMPT_RT enabled kernels and switch between "full" and the "lazy" > mode(s). Right. > On PREEMPT_RT enabled kernels with PREEMPT_DYNAMIC the UTS_VERSION > string is set to PREEMPT_RT and PREEMPT_DYNAMIC is not exposed. Is this > on purpose or just happened? I noticed it, didn't care and promptly forgot about it again :-) > Clark was asking for a file to expose whether or not PREEMPT_RT is > enabled and I was pointing him to UTS_VERSION but then suggested that it > might be possible if we expose the current setting of the preemption > model and use this. > But with this it won't work. > I am not sure if PREEMPT_DYNAMIC is needed to be exposed and if > everybody is happy parsing UTS_VERSION (we used to have a > /sys/kernel/realtime file in the RT queue). Yeah, IDK. This is all just pick a colour :-)