From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 9E2561D0167 for ; Wed, 4 Sep 2024 13:41:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725457321; cv=none; b=fNlYSJlEHGhscES6tAg8OOiyuhWVLseNgZmtFbyqnRchzXi8HVN0EPM5C1/PK6zRTc4GYs5FN3enn9ovK05PjJA26aOZZ/vY+wk25dsCbc4Mgknix22ScaEPOQdyVOP9oZLL6yP7h6e1z4hiefQWyNJ0FAD8XwZuNuS9HnHh+Qc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725457321; c=relaxed/simple; bh=JbWayupVn/JJ7GNhAx0PUBZWkZNObgTS/i31L2CJTQY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Xzzr+UGWu+2US6kaR2vvtjZ2TM6jrGztJWmvEn/hNydr4zHCmALBWTwZlsz/6oDtBcmRJmN92OH3HOZcnZX2LVi4SU9qg0nPS5ZZ15Tw+rNfUz2wKuyxMj4u+OMvOybCTVnzaGHHUvrgUw5lskya4bw/p8PsbD9UTmqEU1MXRoo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=Uxg+LQO3; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Uxg+LQO3" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1725457318; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2MQR4Ycby6XUOwft8GVXSA68r8M0SwRZCOvfGY+GmZU=; b=Uxg+LQO3612JDf7p94Cm708lxxJ5VFk4hifLCA23OVbuslHzt67B+WtjacfL01BRqQqL+5 VobSvOPJt2ZhNrumw2VGGdPsLfRSOw9nsuWgk0X57B3AXEaJBp51p6SCHeNeeCzQOE7c0T FVWhR8wrCjy6wK5JPkloiXtGhOQkk+Q= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-517-mr4fRSDbOuCOEQiSnaZwcQ-1; Wed, 04 Sep 2024 09:41:53 -0400 X-MC-Unique: mr4fRSDbOuCOEQiSnaZwcQ-1 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 86F72193E8F9; Wed, 4 Sep 2024 13:41:51 +0000 (UTC) Received: from [10.2.16.172] (unknown [10.2.16.172]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id B10941955D4F; Wed, 4 Sep 2024 13:41:36 +0000 (UTC) Message-ID: <00df81bb-8790-44c1-8f22-f24b73fb734f@redhat.com> Date: Wed, 4 Sep 2024 09:41:35 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] sched/isolation: Add HK_FLAG_SCHED to nohz_full To: Peter Zijlstra , Frederic Weisbecker Cc: Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , linux-kernel@vger.kernel.org References: <20240818234520.90186-1-longman@redhat.com> <20240818234520.90186-2-longman@redhat.com> <7fa3dbd5-7c2e-4614-a5f4-258546cb090b@redhat.com> <4822d111-b02d-469a-a457-46392c35021f@redhat.com> <20240904130445.GI4723@noisy.programming.kicks-ass.net> Content-Language: en-US From: Waiman Long In-Reply-To: <20240904130445.GI4723@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 On 9/4/24 09:04, Peter Zijlstra wrote: > On Wed, Sep 04, 2024 at 02:44:26PM +0200, Frederic Weisbecker wrote: >>>> I'm a bit scared about rule 1) because I know there are existing users of >>>> nohz_full on multi-CPU domains... So I feel a bit trapped. >>> As stated before, this is not a common use case. >> Not sure and anyway it's not a forbidden usecase. But this is anyway outside >> the scope of this patchset. > Most crucially, it is a completely broken setup. It doesn't actually > work well. > > Taking it away will force people to fix their broken. That's a good > thing, no? It will be hard to take it away without a good substitute. This is exactly what I am trying to accomplish with the dynamic CPU isolation work. > >>> The isolcpus boot option is deprecated, as stated in kernel-parameters.txt. >> We should undeprecate it, apparently it's still widely used. Perhaps by people >> who can't afford to use cpusets/cgroups. > What is the actual problem with using cpusets? At the very least the > whole nohz_full thing needs to be moved into cpusets so it isn't a fixed > boot time thing anymore. Right. >>> My plan is to deprecate nohz_full as well once we are able to make dynamic >>> CPU isolation via cpuset works almost as good as isolcpus + nohz_full. >> You can't really deprecate such a kernel boot option unfortunately. Believe me >> I wish we could. > Why not? As I said, the only thing that's kept it around, and worse, > made it more popular again, is this nohz_full nonsense. That never > should've used isolcpus, but that's not something we can do anything > about now. > > Rigid, boot time only things are teh suck. Declaring a feature as being deprecated is the first step in the process of removing it. Users can still use a deprecated feature as the code is still there. The actual removal will be at least several releases later if not more. Cheers, Longman