From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 E3A80347BC9 for ; Thu, 19 Feb 2026 15:28:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771514921; cv=none; b=nad71iTl0EE0dosd2qA8XB9tezH+wY2vOyClKAgI52LqU9HtTZyRSncPvqisTu3iKaS83uHn+j/WRADrF7KEmM845VWnk0sh+qZTm5j3ziDWCae1Nscq0TCSz3sYa2az/rQBIlKgRr4xbphzjM6aWcS0IE3YzGl905DGwyDorZk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771514921; c=relaxed/simple; bh=rtR+KzzxzKBYIqWs3B0KVmtFGefZcqWIU6doNPDIn3U=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=O/fB2LSj+Tgs+odxKo7XDGkX1xZ+J85IXRHEFhAOiFnnUvZ5s1ufxLzCrb9ra23KOQudqfTyXCc101fJKcu0Zt74uEvLIeFwjVezKikzEYT1XnrVO1sNCQMy0wzrZNlRLiziSgXHu4oDI2sj1jkI1owwScSH0s7aKL/aMjkNSWE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine 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=gg2Uv3Mq; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine 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="gg2Uv3Mq" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1771514919; 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: in-reply-to:in-reply-to:references:references; bh=B/MYhX9u18ZxQhXovryB0Eh7LFOheskfwpriZ+MbSug=; b=gg2Uv3MqCm9gXOWpsfOgholmi+rDFArv1CkBkkALQ/4fP1HWSH2w3ZpaF/xaoo5tHDa92g e9UBbntKfLkS66lztatCS4Oy0wSgjAZ1c7MrX+tpnBJNUa3v/tR1ou//7IKM7c+KP3+/ou WbgXVoNbk40Sgp0eENwmLcjGkCTtffU= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-488-nuJ9k3mtMk66GG3N1gk6Ew-1; Thu, 19 Feb 2026 10:28:33 -0500 X-MC-Unique: nuJ9k3mtMk66GG3N1gk6Ew-1 X-Mimecast-MFC-AGG-ID: nuJ9k3mtMk66GG3N1gk6Ew_1771514909 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 6BC7E18002DE; Thu, 19 Feb 2026 15:28:28 +0000 (UTC) Received: from tpad.localdomain (unknown [10.96.133.5]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C87211955F22; Thu, 19 Feb 2026 15:28:26 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id BC8EE401E2101; Thu, 19 Feb 2026 10:15:41 -0300 (-03) Date: Thu, 19 Feb 2026 10:15:41 -0300 From: Marcelo Tosatti To: Michal Hocko Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Johannes Weiner , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Leonardo Bras , Thomas Gleixner , Waiman Long , Boqun Feng , Frederic Weisbecker Subject: Re: [PATCH 0/4] Introduce QPW for per-cpu operations Message-ID: References: <20260206143430.021026873@redhat.com> Precedence: bulk X-Mailing-List: cgroups@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: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On Wed, Feb 11, 2026 at 05:38:47PM +0100, Michal Hocko wrote: > On Wed 11-02-26 09:01:12, Marcelo Tosatti wrote: > > On Tue, Feb 10, 2026 at 03:01:10PM +0100, Michal Hocko wrote: > [...] > > > What about !PREEMPT_RT? We have people running isolated workloads and > > > these sorts of pcp disruptions are really unwelcome as well. They do not > > > have requirements as strong as RT workloads but the underlying > > > fundamental problem is the same. Frederic (now CCed) is working on > > > moving those pcp book keeping activities to be executed to the return to > > > the userspace which should be taking care of both RT and non-RT > > > configurations AFAICS. > > > > Michal, > > > > For !PREEMPT_RT, _if_ you select CONFIG_QPW=y, then there is a kernel > > boot option qpw=y/n, which controls whether the behaviour will be > > similar (the spinlock is taken on local_lock, similar to PREEMPT_RT). > > My bad. I've misread the config space of this. > > > If CONFIG_QPW=n, or kernel boot option qpw=n, then only local_lock > > (and remote work via work_queue) is used. > > > > What "pcp book keeping activities" you refer to ? I don't see how > > moving certain activities that happen under SLUB or LRU spinlocks > > to happen before return to userspace changes things related > > to avoidance of CPU interruption ? > > Essentially delayed operations like pcp state flushing happens on return > to the userspace on isolated CPUs. No locking changes are required as > the work is still per-cpu. > > In other words the approach Frederic is working on is to not change the > locking of pcp delayed work but instead move that work into well defined > place - i.e. return to the userspace. Michal, I can't find such work from Frederic. Do you mean: Subject: Re: [PATCH v6 00/29] context_tracking,x86: Defer some IPIs until a user->kernel transition >From Valentin ? Or if you have a pointer to Frederic's work. > Btw. have you measure the impact of preempt_disbale -> spinlock on hot > paths like SLUB sheeves? Doing that, will post results as soon as possible.