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 DAEFE13C677; Mon, 24 Jun 2024 12:41:25 +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=1719232887; cv=none; b=A37ylm7NUeIscg5PaqgftskAH+kTxBn7W1BGJNOsXo0cG2XxBlV5NhNv+Zqs1oZVeWz6pyNC9peO2LeXKC9Igk1ZLXIc1gKj9htaJLfTfNZ0sXhdUc45ioookZxwGG4vD7DoKhhrA/oCgUdPBB+4ARbxIKv4fHuJ03gsc7B48BQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719232887; c=relaxed/simple; bh=hqF5YhKcz6BXATHeicfIAP7R6xcFWkNdFhorTxOChFc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=de+xVoGMXZR9mmfQkh82F997uhlA/vR4xQBvm4cGb0PKA5kLQ8SGYRcb7hLdmcstRTEBBcqdj41kNCylFK3aodtHaqQQ6bsaIaBFj3bWC51yoYfAI3bv5PLyZHg1uPThKP1MuHmBcX9VuBNkNzUh/Gi/HFV7a5BCJzOO90TevFA= 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=URarxOO/; 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="URarxOO/" 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=hqF5YhKcz6BXATHeicfIAP7R6xcFWkNdFhorTxOChFc=; b=URarxOO/eoOmOCkGprP4MsHkO2 Z1bpQXKwcHb/4eAWT+taPhSuzOTJVvmwbjqqIHeqT5tVTBmWkpMJbgy3cxllqFCLJpaISzFcWyj1Z jZ8RBWZVjxbNwiNT4Fv7apbPWy3shPuVe3cixSbpw49Mu1TLKVXPtDoi0WZerdUAG/gWH8Zbln36r PgRhgqIyRoA/BvQ5msnkcL89rv+DGqkKpfP2GJBkHqin4kZmZUk4+ll7FinPx87MWdUimAjP7rMi3 13SM2uhjgs+auumvXHXP9BxWrtbwUorBesDHck+F6bzTvgD4p1BGcKfVtnMWWbYCcjmv6IPJREMQS sUFLunXA==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.97.1 #2 (Red Hat Linux)) id 1sLj0A-00000008FAl-3Jje; Mon, 24 Jun 2024 12:41:00 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id CD4EC300754; Mon, 24 Jun 2024 14:40:53 +0200 (CEST) Date: Mon, 24 Jun 2024 14:40:53 +0200 From: Peter Zijlstra To: Tejun Heo Cc: torvalds@linux-foundation.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@kernel.org, joshdon@google.com, brho@google.com, pjt@google.com, derkling@google.com, haoluo@google.com, dvernet@meta.com, dschatzberg@meta.com, dskarlat@cs.cmu.edu, riel@surriel.com, changwoo@igalia.com, himadrics@inria.fr, memxor@gmail.com, andrea.righi@canonical.com, joel@joelfernandes.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH 18/39] sched_ext: Allow BPF schedulers to disallow specific tasks from joining SCHED_EXT Message-ID: <20240624124053.GN31592@noisy.programming.kicks-ass.net> References: <20240501151312.635565-1-tj@kernel.org> <20240501151312.635565-19-tj@kernel.org> Precedence: bulk X-Mailing-List: bpf@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: <20240501151312.635565-19-tj@kernel.org> On Wed, May 01, 2024 at 05:09:53AM -1000, Tejun Heo wrote: > BPF schedulers might not want to schedule certain tasks - e.g. kernel > threads. This patch adds p->scx.disallow which can be set by BPF schedulers > in such cases. The field can be changed anytime and setting it in > ops.prep_enable() guarantees that the task can never be scheduled by > sched_ext. Why ?!?! By leaving kernel threads fair, and fair sitting above the BPF thing, it is not dissimilar to promoting them to FIFO. They will instantly preempt the BPF thing and keep running for as long as they need. The only real difference between this and actual FIFO is the behaviour on contention. This seems like a very bad thing to have, and your 'changelog' has no justification what so ever.