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 D95A128750A for ; Wed, 7 May 2025 13:40:26 +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=1746625226; cv=none; b=bxtn93B+p40NQjjCki2edTKpZA8Yffzc9ovsWmP0Rg+D2rvb3wK/T0intIFRyOsuD0WzMqzDyRt7oUifXl+kDdepxqZBXfjCwQlqQncNEI8jHY8emrFUfhh/MnffVyrW2I8yn18bmhDTvxQYHlGCFeotOUuMm15L/k5OsnYuicA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746625226; c=relaxed/simple; bh=gWnfKNZyzMrtzpRcUWQ2mVL8CbobfVNiC5GlA7+/iZU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=BszlkkbmJUkVMyyPgtjlQviXyoO8F6eXNMZQKqLJlmHCO/G5EWMr8+QLR96ODGxxm4Ql9ffdaoFCtZxg6tgJHyMwBf7RcSt+sYlgV6GyZUY+zNFh7km5q1eFkEsfdsPU+9D8E+HCnewmsehWaVEWWp793EJ5bNPa0yG65ElYCL8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kynczDTw; 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="kynczDTw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 60139C4CEE7; Wed, 7 May 2025 13:40:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746625226; bh=gWnfKNZyzMrtzpRcUWQ2mVL8CbobfVNiC5GlA7+/iZU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=kynczDTwdqOU1zA8lexp1K4KyhEEF+9ptTfE/o6NKytQfltUbOs9NJdC0PGuWS+jZ cOU+F/3OwKWFz3kDcU7VNeh+E1Wy7juic3nZao4Oy6KqGB1Va/6QWZWq4AjDfNmPfA J1tKdHx3SBvMPhC8UKWLcJfCky+JFpYUuvTXjiKMRmn/CvSfMhWSRF7vtqhOtnlj41 sjBYbsnRchYdwdn7HYN5kBeUBFGGjTisd1gXwh/r1Vubhl+cbFMDqkMoGcc2TkYGeJ v0ESk/w9UKq71rhmR2RARVGDtiSN4Jpqsvp4oMXuqvxqtyodRMiei5DnCbX0pMxllh G2XAW/t1ZimwA== Date: Wed, 7 May 2025 15:40:23 +0200 From: Frederic Weisbecker To: Gabriele Monaco Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Waiman Long Subject: Re: [PATCH v4 2/5] timers: Add the available mask in timer migration Message-ID: References: <20250506091534.42117-7-gmonaco@redhat.com> <20250506091534.42117-9-gmonaco@redhat.com> <3f54534266f4405fc3c6943599edd9be88becd57.camel@redhat.com> <9b96acdb43b80f067a34b83c5fe9fc3e79f1e3a4.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: <9b96acdb43b80f067a34b83c5fe9fc3e79f1e3a4.camel@redhat.com> Le Wed, May 07, 2025 at 02:46:39PM +0200, Gabriele Monaco a écrit : > > I'm not so sure about this one though. > As far as I understand [1], is preventing the user from setting > different CPUs while doing isolcpus=nohz, and nohz_full= (which is now > equivalent). But I seem to be able to do isolcpus=0-3 and nohz_full=4-7 > without any problem and I believe I'd hit the issue you're mentioning. Duh! > (The same would work if I swap the masks as 0 cannot be nohz_full). Unfortunately 0 can be nohz_full... > > # vng -a isolcpus=0-7 -a nohz_full=8-15 head > /sys/devices/system/cpu/{isolated,nohz_full} > > ==> /sys/devices/system/cpu/isolated <== > 0-7 > > ==> /sys/devices/system/cpu/nohz_full <== > 8-15 > > (where probably some CPUs are set up to do housekeeping stuff anyway, > but if we just look at the masks, we won't notice) > > Then I assume this should not be allowed either, should it? > Or am I missing something here? Exactly then. housekeeping_setup() already handles cases when there is no housekeeping left. I guess that section could be made aware of nohz_full + isolcpus not leaving any housekeeping left. > > > > > But if nohz_full= is passed on boot and cpusets later create an > > isolated > > partition which spans the housekeeping set, then the isolated > > partition must > > be rejected. > > Mmh, that would make things easier actually. > I assume there's no real use case for that kind of hybrid setup with > half CPUs nohz_full and half domain isolated.. I guess we can accept nohz_full + isolated partition as long as a housekeeping CPU remains. Thanks. -- Frederic Weisbecker SUSE Labs