From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 7C8D3320F; Tue, 8 Oct 2024 10:54:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728384881; cv=none; b=b8pJiFYFMoekK1fPca5zs3mJlIfuRgoma2zeJkMgLMMRWwLmvTbc8fCT6tohOPuBwbGTjnrwLeb3NdFlXf5aSmDcYiwGVXWUUmU62ebvoQLMMd/Baz/sg4hUdLB0Tnq74TrJ+aXBszmD2waCl7pnSDqQ65Z68FT1p4EsLEv0VV0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728384881; c=relaxed/simple; bh=tMLwLbqSfjHfOw4e2UN9i2C4GUC3GQ+xO7cRITf7Dtw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=qOTJMHLl0NDXk8x1uff6z8X+2aCZ9YxbsQLyx7j39438f/SB4lvll5PBjyqx9A20wAL94CZNUqbWdA7s6uYDeipDqmGHapT3TsfhDe/Yd+Ywvd+Uzmd6EaPT6fX+PkZyl3lrK2iNOeiJ+0t6HcVYgIGSgoFl5l7xcV5vxvCHgIo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ovbgNVzJ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ovbgNVzJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6557DC4CEC7; Tue, 8 Oct 2024 10:54:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728384881; bh=tMLwLbqSfjHfOw4e2UN9i2C4GUC3GQ+xO7cRITf7Dtw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ovbgNVzJkmgwqhNXgMxucWth9ib2ZNZ6+KFUe3Jx7Xyld3/TxQ48FYFAUUNLlICTc yFadogOuiCYTIGm+UsXdxL1o2OtGyT/PB3X4e2K+e2iGN0Inm7DUo3hPCZ9yKyvMjk UCkMz7kYkiJeWmDg6VSfATI0zNPqrmcBOYRHAKN3S5yDu7ILX+HO298ngo7uT0ZCwQ ykVBmjDBpX7VH1/p2o4V5KCpjt2r5OzRGtHldp6WZalqFYpJdegy3OrkRlZcwuiqsm InKMMt+8ap7bWGNYZqTqe4AZZ3GjcU50a3AgX/RH5wAK5LjGoMh8WO/cNCO/BzmEDI Vq9L+nSAWj39Q== Date: Tue, 8 Oct 2024 11:54:35 +0100 From: Will Deacon To: Frederic Weisbecker Cc: LKML , Peter Zijlstra , Vincent Guittot , Thomas Gleixner , Michal Hocko , Vlastimil Babka , "Paul E. McKenney" , Neeraj Upadhyay , Joel Fernandes , Boqun Feng , Zqiang , Uladzislau Rezki , rcu@vger.kernel.org, Michal Hocko Subject: Re: [PATCH 11/20] sched: Handle CPU isolation on last resort fallback rq selection Message-ID: <20241008105434.GA9243@willie-the-truck> References: <20240926224910.11106-1-frederic@kernel.org> <20240926224910.11106-12-frederic@kernel.org> 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: <20240926224910.11106-12-frederic@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) On Fri, Sep 27, 2024 at 12:48:59AM +0200, Frederic Weisbecker wrote: > When a kthread or any other task has an affinity mask that is fully > offline or unallowed, the scheduler reaffines the task to all possible > CPUs as a last resort. > > This default decision doesn't mix up very well with nohz_full CPUs that > are part of the possible cpumask but don't want to be disturbed by > unbound kthreads or even detached pinned user tasks. > > Make the fallback affinity setting aware of nohz_full. This applies to > all architectures supporting nohz_full except arm32. However this > architecture that overrides the task possible mask is unlikely to be > willing to integrate new development. I'm not sure I understand this last sentence. The possible mask is overridden for 32-bit tasks on an *arm64* kernel when running on an SoC featuring some CPUs that can execute only 64-bit tasks. Who is unwilling to integrate what? Will