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 21DB428ECE0 for ; Tue, 24 Jun 2025 14:52:32 +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=1750776753; cv=none; b=asyflgViWssQQ71qh1XAnAEz4/++OT4crs+uom8inLs0F9pn2dR4yQKbtZNQXbEeDj9CyFmF4rVSEqdrLc1YHwYExGK7FUEBvkun3qflgH75J46IJSmMuEO5Jumen8BbtVOESkuw1aAlW8e322wtgEbcxbHmPyxz3uEhd9Bk0dk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750776753; c=relaxed/simple; bh=ceUCtSYWiIlQmuJ0bYheOpHsWDwbZ/a/I0j7HVRa43g=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=l5XFc5zYjGUGTFMQMfGXup0kLKWfXP6NmHIN7BzKPpA1zZLOGkND1tovT+GR9ZdVG33L7zkbL61D7vzUjtVXWJcJy7eMvtCtiPlvyj+jKf4jZBUBYD5P0E7Ezx0d38wr7yS94bBFIF94tmcN8vhhKdAxwQ4zBJvytn06hiPUQ5w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Q9fNB0DZ; 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="Q9fNB0DZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5CF7BC4CEE3; Tue, 24 Jun 2025 14:52:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1750776752; bh=ceUCtSYWiIlQmuJ0bYheOpHsWDwbZ/a/I0j7HVRa43g=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Q9fNB0DZUr1xiaknhEWKMnn53zVOJchtoC02SLDnCq/bg5lcbK/1jG0Ie0wbxbDMq BRgsyPryrczw7RDsNfL1HTSeuQ35cpy9F+/f+2x31BUN5Fc7Dl8Qsbir2cjjs/gBel C/4cxjthlZDIytlNeh5pM/RbRzxenLXuM4IP4/SYBa8Bxmmtw7R1NR4tlI0E1tv5UC Wl+R3D57fZiE/fEU/nfT4i/ZujL5A4fz7gZTlA6mau6fouJreINHnOYbWAH3wMEB3X DluZvqlOKzze2IP1RuLwIdk1o/45vCFZL8ZnodVbhyKXAtHsaLIqNFSS481ys+Wlfs x/lUyw7YZAqVA== Date: Tue, 24 Jun 2025 16:52:30 +0200 From: Frederic Weisbecker To: Gabriele Monaco Cc: Thomas Gleixner , linux-kernel@vger.kernel.org, Anna-Maria Behnsen , Waiman Long Subject: Re: [PATCH v6 6/6] timers: Exclude isolated cpus from timer migation Message-ID: References: <20250530142031.215594-1-gmonaco@redhat.com> <20250530142031.215594-7-gmonaco@redhat.com> <875xgqqrel.ffs@tglx> <878qlhnunz.ffs@tglx> <1bc41a7a5bd46860318b0417fa27121758f28448.camel@redhat.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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1bc41a7a5bd46860318b0417fa27121758f28448.camel@redhat.com> Le Tue, Jun 24, 2025 at 04:06:41PM +0200, Gabriele Monaco a écrit : > Right, but as far as I understood, the first call to > tmigr_set_cpu_available() happens after the isolcpus parameter has been > parsed so we know at least cpu0 is going to be isolated. > > On my machine it works reliably this way. I'm a bit lost in the init > code but seeing housekeeping_init() before rcu_init(), which in turn > should be required for some RCU-related early_initcalls, makes me > believe this order is guaranteed to be respected. > Or am I missing something? Right I think you need to keep those checks because if CPU 0 is isolcpus and CPU 5 is nohz_full, CPU 0 will become later the timekeeper and must stay in the tmigr hierarchy. OTOH if CPU 0 is isolcpus and there is no nohz_full CPUs, then CPU 0 doesn't want to go to the hierarchy. cpuset isolated partitions are different because they issue SMP calls whereas isolcpus is defined on boot. An alternative for isolcpus could be to make a late initcall and do the smp calls from there just like is done for cpusets. Thanks. -- Frederic Weisbecker SUSE Labs