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 763E628D84D for ; Thu, 10 Apr 2025 14:43:52 +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=1744296232; cv=none; b=BAJL8aqgiY7h+X9NgcKHQhqp60FYp7s/O2di0bdVsaeTN7uWlD0AVOsj+pynu9NacY4E21K/aIrHGKtheBRNY0w4CPMxkBjFVk397HDGSwdHw57OWxtug2kqduMe/vWr5aRP4+NxVD7q45dabnojZT9IEXmyjZ7jIEvfhPd+y4c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744296232; c=relaxed/simple; bh=xAuiSTkrkcSKLugsuwfGK1c08uM4VX03pD0uOicYexM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=S5Kb7fuhqXPgBeDpj7pQ6i6kFhBB2w0i8tadHcJkUIYnj4yCkp5ncxzEhfLCGHsrcxzaEDYdfbR6A8pZqjL/bI9C+trV9LAdgojdIJT5OJ89lgRG6EvU6pfJYU7wbzS6WirYbJQDIENC4eui8YtZqN390IPwBurect/AhzsR2D4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TKYwo7gX; 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="TKYwo7gX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A83D5C4CEE8; Thu, 10 Apr 2025 14:43:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1744296232; bh=xAuiSTkrkcSKLugsuwfGK1c08uM4VX03pD0uOicYexM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TKYwo7gXgoy2zEs/AJFN2YufvqNd9Lo0y8zN9OUuNmYu5xsOOhGRdE8HkhsqCsMnM bTOQjMEIc2PjhBP8abrHHF4HZpyppkSPlxSO/evkbAvcDQdQP9C34o0jthwUR5eW8T CIVdoIc5bsChCUJyIF7+8Kq8Uw2deYQyHgC2KtWUsWnSdDhEGrNTnujiMmhENea7hS f4lyLijI/WAvWUhBDvt+G7X531U5j2uzoTWxxIzfldjxiXz+G1U2PtmeyCJ2qVigD0 aQiw/WmglLtqX/TPzEt5GHo+KsXSKSIyuy1z9aYKEmJQf8ZAa6iOyg3PWJM31Ruo9G vWnXQ+yxuYh3A== Date: Thu, 10 Apr 2025 16:43:49 +0200 From: Frederic Weisbecker To: Waiman Long Cc: Gabriele Monaco , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: [PATCH] timers: Exclude isolated cpus from timer migation Message-ID: References: <20250410065446.57304-2-gmonaco@redhat.com> <87ecy0tob1.ffs@tglx> <2c9d71fd79d7d1cec66e48bcb87b39a874858f01.camel@redhat.com> <77988036-7550-4ee2-a738-9f9bd4417001@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: <77988036-7550-4ee2-a738-9f9bd4417001@redhat.com> Le Thu, Apr 10, 2025 at 10:35:55AM -0400, Waiman Long a écrit : > On 4/10/25 9:03 AM, Frederic Weisbecker wrote: > > Le Thu, Apr 10, 2025 at 12:38:25PM +0200, Gabriele Monaco a écrit : > > > On Thu, 2025-04-10 at 10:26 +0200, Thomas Gleixner wrote: > > > > How can that happen? There is always at least _ONE_ housekeeping, > > > > non-isolated, CPU online, no? > > > > > > > In my understanding it shouldn't, but I'm not sure there's anything > > > preventing the user from isolating everything via cpuset. > > > Anyway that's something no one in their mind should do, so I guess I'd > > > just opt for the cpumask_first (or actually cpumask_any, like before > > > the change). > > With "nohz_full=..." or "isolcpus=nohz,..." there is always at least one > > housekeeping CPU. But with isolcpus=[domain] or cpusets equivalents > > (v1 cpuset.sched_load_balance, v2 isolated partion) there is nothing that > > prevents all CPUs from being isolated. > > Actually v2 won't allow users to isolate all the CPUs. Users can probably do > that with v1's cpuset.sched_load_balance. Perhaps, and I think isolcpus= can too. -- Frederic Weisbecker SUSE Labs