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 BB2DF2D97BA for ; Thu, 25 Jun 2026 08:42:43 +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=1782376966; cv=none; b=Phf+LHHozkfYAfP9e3t1a7j9g2h4StB4juDfz9UdkU3r83X+P54KdJUrjHS79kFWLX6tLoYjtBr0NylFSbG4lj9PSdmyXn5Uk6U5I+JRs775LYgXfQiifedg3ktrn88iHZW28IwvRqBDT3NX56zyMQB22nt2cmdpjiAFY6Nkxu8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782376966; c=relaxed/simple; bh=LHlQ+qy7b393T66T/tfXi9AY94RdbsdikRONOkCUKtc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=OpOwTm4+hFP6MnAfKQr/djaM5or73MzwFh3jU7eyB+leYWezFWWoJdsj7i/ZRBuxSMn3M5dxJJ7ROFlwQ+RYW8e/LH0NFmAlO3DFT4HnevBSFGUWkK2Th6nZnPTGO65YoORdaoSrCtxibBoledQ3sfpoIrHUxe5DUJ9s0DRds4E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=APf2rWmq; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass 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="APf2rWmq" 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=V8tf7IhTHW/8oTNNWj2v6XkA/E7I5UX98MrXSuosKCk=; b=APf2rWmqW2BG3fUiW2RwH9OOwj kuXJ6vpvkd7JTivvaJI6ALPV6FG+Cp61zt63LI1xOvQ5NYJyCbm+gfeETOF1oDzv6ZFZGezsadt7N Zk5XDigKltVb9ytctlDeNAmPHI8ijVoKU3sQwidnMQhdRDdFQ9we/QylJPYTGjk8HGs6q5r3WJ01A y51gT52xbRDgiuD2i7EDtBBwITRefJAEMlwYeEU2svVognnCXONw0Pb855il6IvQiDZYerD6rcaSu YjDtLPLIUs4QMEgacaIDeM8RppKRjFpq4sGXWqwyOZv4IgxvMroCoVHUNoilpqaLH25yDpGc4p0Mr w8rgcofw==; 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 4.99.2 #2 (Red Hat Linux)) id 1wcffI-00000003NBr-2myb; Thu, 25 Jun 2026 08:42:28 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 19F05300B5F; Thu, 25 Jun 2026 10:42:27 +0200 (CEST) Date: Thu, 25 Jun 2026 10:42:27 +0200 From: Peter Zijlstra To: Jianyong Wu Cc: mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, sshegde@linux.ibm.com, linux-kernel@vger.kernel.org, yu.c.chen@intel.com, tim.c.chen@linux.intel.com, justin.he@arm.com, zhongyuan@hygon.cn, yingzhiwei@hygon.cn, huangsj@hygon.cn Subject: Re: [RFC PATCH 0/8] sched: Extend cache-aware scheduling into topology-aware scheduling Message-ID: <20260625084227.GS42921@noisy.programming.kicks-ass.net> References: <20260625030759.25928-1-wujianyong@hygon.cn> 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: <20260625030759.25928-1-wujianyong@hygon.cn> On Thu, Jun 25, 2026 at 11:07:51AM +0800, Jianyong Wu wrote: > The current cache-aware scheduling implementation adopts an > LLC-centric task aggregation model. While effective for workloads > that fit within a single LLC domain, this design is fundamentally > limited by a fixed aggregation scope that cannot scale across > scheduling domains. > > This leads to a single structural limitation: the lack of > topology-scalable task aggregation. When workload size exceeds > the capacity of an LLC domain, the scheduler cannot extend > aggregation to higher-level domains, and locality cannot be > preserved effectively. At the same time, higher-level topology > information such as NUMA domains cannot be consistently utilized > for placement decisions. > > This patch set addresses this limitation by extending > cache-aware scheduling into topology-aware task aggregation. > The aggregation scope becomes hierarchical and can dynamically > expand or contract across scheduling domains based on workload > demand. > > Task aggregation starts at MC or LLC domains under light load, > and expands to NUMA and higher-level domains as load increases, > and contracts when load decreases. Urgh,... that only really works if the topology has a low branching factor. I would much rather see things move towards a mask of cache domains, rather than any single one, where the number of bits in the mask is minimal vs the concurrency. This has already been mentioned a number of times, which seems to suggest you've not actually been reading along very well :-(