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 CB48E1B0405 for ; Tue, 18 Mar 2025 06:38:52 +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=1742279934; cv=none; b=N+O4Dyo71tkkzvLOX15/n6mj6hixVs3gu3176cbnQxfXNGsacLIIYuj5FHiu/YWYImUX7om40Z5L+DEtvsjH12PdtpI2Hy09zmuyk0esy1PyL+qpJ3WdrgYrj2Sh4BPp34erlKKhPJ5Ae91NMgyaAMVU0vsLtLmE/gpVQx/5MVg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742279934; c=relaxed/simple; bh=Xkd1W54+skof31D5Vc9HPZLsP4UXaU3m4a6f14pbjC4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=m+ugPx79xw4j++gep8LagkghMtwHCpJH0iVMoA5f+Yp6vxATNlRs9XtphQysCdL3NWpmUumjbM3olk4NVzszJqChm8fefiN4i2rJcJ/clDf+uKTu9QJwnWA49PhhpqUGfpMVr8zHdiwaT3pKU3A6ompBQ2aERtcE35DVeYXUNbc= 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=pyD3dKuo; 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="pyD3dKuo" 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=NoDvENuzewtlToC01BvX2rAwwlEM3FbInPo863Y2sHc=; b=pyD3dKuoMptDM5o7Pm/lyoi78c pX62Vrp6GOagk2NJA/OUX5gpKZyJqMvMqyfmEcnL9Io05cgPNDsxYkRKzo/Fsy6/ZDm4MZXhZXOJI CdB+dDdEw+azE9JRP9w7ykHbnRpDFnzoI076TcP7F1A3RJE04ff+LOfpttR05xBBCfqrYuteCh/XL gfOHG8dk7VZa+Hnm0IBp+yRracrRDWB/W6NRpiXpWQBNXxvLOkT9gqIJjxi1Du7LW9rSIhvFU75sE Zwi/LsLlUiUGCldHaQR9fCooMHV6aJqRXGIGsrAl+liyhDrJq6BX7gQV3IWsZScbWuRrba9LfR4JV Owwzlygg==; 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 (Red Hat Linux)) id 1tuQbA-00000003hUU-1g21; Tue, 18 Mar 2025 06:38:48 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id F26E0300783; Tue, 18 Mar 2025 07:38:47 +0100 (CET) Date: Tue, 18 Mar 2025 07:38:47 +0100 From: Peter Zijlstra To: Jianyong Wu Cc: mingo@redhat.com, vincent.guittot@linaro.org, jianyong.wu@outlook.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] SCHED: scatter nohz idle balance target cpus Message-ID: <20250318063847.GA25930@noisy.programming.kicks-ass.net> References: <20250318022358.195154-1-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: <20250318022358.195154-1-wujianyong@hygon.cn> On Tue, Mar 18, 2025 at 02:23:58AM +0000, Jianyong Wu wrote: Re subject; if you look at other patches for sched, you'll note that we do not capitalize it. Also, what you're doing is not scatter, it is rotation. > Currently, cpu selection logic for nohz idle balance lacks history info > that leads to cpu0 is always chosen if it's in nohz cpu mask. It's not > fair fot the tasks reside in numa node0. It's worse in the machine with > large cpu number, nohz idle balance may be very heavy. Since you seem to care about ilb and numa; there is this _very_ old patch set that never got finished: https://lore.kernel.org/all/20091211013056.305998000@intel.com/ IIRC there was a problem where it would simply stop running the per-node ilb when the node went idle, leading to node level imbalances. This should be curable by picking one such idle node and keeping its ILB active or somesuch. Something to poke at if you're interested..