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 10AE725A33A for ; Tue, 1 Jul 2025 10:57:01 +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=1751367423; cv=none; b=oFF7DwRx4DKIf06gEpvaXzcf+C3Xj9GYl6jxYMb9uOQCqbWaa97XD2FD8TxAV4TQ2JV1Y99Rs5UjgVrhq1dh3qFt5plRdz0Epyw0fOdPC0r6GAWrfiuaXyKJBPkX+Nyd4W5FjB7pSxiWe6kayu81GEPX5OvUH0JqlYakBaPmjaQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751367423; c=relaxed/simple; bh=oggiuRkpsfgjptBqTHTgT0syKqEumoLD0QCF4biYLCo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=kPEqXadNXceMFU04B72bVPnLMJCHfYEMPeDRqBg9GhIyqfIlFdamDSMJFr5aA80mbUsMIu6fH6c8u0+RY7s9WHoRP1am2Y3f8gzcG+tk/fuvgriNSuJZT8+AVo2qiVkrSPn2qY3ZxoUQ2qckeBeADjQfK4KfdMUt+NE+8+bR28Q= 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=jdrkgKK7; 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="jdrkgKK7" 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=oggiuRkpsfgjptBqTHTgT0syKqEumoLD0QCF4biYLCo=; b=jdrkgKK77zQJcqDsyCPNzigcRV gE1a2ycBy1eSSAOJ2xg01b9DSOaJZu2OcvFTkBzMcim7YX+4Z70MCIzzA607Bsj80ynZRYcUQsiIs 1yMtxG+vtspvnHUQtwPrnIGbBpMY0pOtdksDHr3IDxpT2ZW4MX/Oc5HHg7MPr25Y/km3cDAlRUXKF jAU85joCn7RZvasJbECBbs+rccwr00vMOxnIYURomgh1JX3Bc7gO0e605n3B2aQT4NiLTLABmFcal yntIuJyGVhF6Esr0wgDRbxHhmysmvvhVP7oxH+xNYc/eQc+DeUUHnYdtgDveko0arZj+2aVj7uZ7m 4BeDGu3A==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1uWYfW-000000074LM-3Yuo; Tue, 01 Jul 2025 10:56:55 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 7DB36300130; Tue, 01 Jul 2025 12:56:53 +0200 (CEST) Date: Tue, 1 Jul 2025 12:56:53 +0200 From: Peter Zijlstra To: Thomas Gleixner Cc: Prakash Sangappa , linux-kernel@vger.kernel.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, bigeasy@linutronix.de, kprateek.nayak@amd.com, vineethr@linux.ibm.com Subject: Re: [PATCH V6 1/7] Sched: Scheduler time slice extension Message-ID: <20250701105653.GO1613376@noisy.programming.kicks-ass.net> References: <20250701003749.50525-1-prakash.sangappa@oracle.com> <20250701003749.50525-2-prakash.sangappa@oracle.com> <87cyakmhdv.ffs@tglx> 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: <87cyakmhdv.ffs@tglx> On Tue, Jul 01, 2025 at 10:42:36AM +0200, Thomas Gleixner wrote: > What's worse is that it breaks the LAZY semantics. I explained this to > you before and this thing needs to be tied on the LAZY bit otherwise a > SCHED_OTHER task can prevent a real-time task from running, which is > fundamentally wrong. So here we disagree, I don't want this tied to LAZY. SCHED_OTHER can already inhibit a RT task from getting ran by doing a syscall, this syscall will have non-preemptible sections and the RT task will get delayed. I very much want this thing to be limited to a time frame where a userspace critical section (this thing) is smaller than such a kernel critical section. That is, there should be no observable difference between the effects of this new thing and a syscall doing preempt_disable(). That said; the reason I don't want this tied to LAZY is that RT itself is not subject to LAZY and this then means that RT threads cannot make use of this new facility, whereas I think it makes perfect sense for them to use this.