From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 1A668248886 for ; Fri, 20 Mar 2026 08:53:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773996825; cv=none; b=EGWY20RkVIUEN4YDdvNZfwdo66qhZTDVKWMN7WBu2s3z7w/ivFyaq7gVs36Kz3zHmL2Aw8GJSScHnUzKmZpPo6O3FiEvoM6dyqdrbw2AGyfi3ithAZ64nO9qUlQh+YLzmBCGx3BwN4bv5fD/oNvkbH/d7dm6VYvpeUbQ4yAFw0k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773996825; c=relaxed/simple; bh=cbuYGnjIL4qZRBuQTxxGc7FEhsAzDvC05YWIfxP3Im0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rAzGQZmQN5kUyG99lgWReBEQjVtPscEwPiQeu4wCN8+/fHZ2xIWs5rMiq7Atc1PgZXnwH3Ji7V3Q/rsBofoQhDkcoD8Z2hRfG7GVU4Ty1Dh/x2YHQTSNxevBfsZDC7SWg5JPLHhQShOKiGnTyLIAowpQl0kC7PDIBGYW7yJyVHk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (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=PGSM/VIH; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (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="PGSM/VIH" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; 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=9FvdlMfeAlQXfWMexp2BIQSQ21HFfgRQsmlCuMZdMrA=; b=PGSM/VIHmR4buaiCJK0CUicAIz 0eIth0oZyq2yKMuQvtWLgv3Hix7L5JSFev+fQfU4lyVMfDllt8Mk4X04lH4uvzr8x2LaPe3Trh/Vx fxBiTdgJz04MIANO1u+RRRD2+MNTJ4lfloguTkrCHKJvF/2Yhwnnwcu62B0P9xQ4GmG4l16aB11U6 1V5GgrwNiUbbz3OQdSmLdBJKLuhQUixj8rtoOKOQcRtIf9vDSg+GItST20eICk0ZZv9Sm7Y+79NCa 5taLo0BBzXPV/I/grBmPpCmO47fRMmzhdwORFeCNTEzp8DwLyAAsxGC/HuFQ4amCW43h6fMHFwa2Y lfrPStNQ==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1w3Vbh-00000007VWG-3Afv; Fri, 20 Mar 2026 08:53:25 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 53198301BDE; Fri, 20 Mar 2026 09:53:25 +0100 (CET) Date: Fri, 20 Mar 2026 09:53:25 +0100 From: Peter Zijlstra To: Chen Jinghuang Cc: mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org, bsegall@google.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, chenl311@chinatelecom.cn, steve.sistare@oracle.com Subject: Re: [RFC PATCH v5 0/9] steal tasks to improve CPU utilization Message-ID: <20260320085325.GM3738786@noisy.programming.kicks-ass.net> References: <20260320055920.2518389-1-chenjinghuang2@huawei.com> 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: <20260320055920.2518389-1-chenjinghuang2@huawei.com> On Fri, Mar 20, 2026 at 05:59:11AM +0000, Chen Jinghuang wrote: > When a CPU has no more CFS tasks to run, and idle_balance() fails to > find a task, then attempt to steal a task from an overloaded CPU in the > same LLC. Maintain and use a bitmap of overloaded CPUs to efficiently > identify candidates. To minimize search time, steal the first migratable > task that is found when the bitmap is traversed. For fairness, search > for migratable tasks on an overloaded CPU in order of next to run. This makes no sense. It is the task of newidle to get more work -- if that is failing for you, then we should fix that, not build a second way to get tasks.