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 E737D3019DC for ; Wed, 11 Feb 2026 16:51:19 +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=1770828681; cv=none; b=Yvz6CUtjRdGqbqk4ZPFHZpVMRsw3EDW7hJQTuMN1zi1Rl5pyaZanTcyFVnlGX5oaJAF9V6mGAucYz20wTw/Bs/S+jR/wdwIUVjllQHN5TlRa1fa40RjYCw5PzAYyRMm+kOfdJjgiE/zyak8l6GqQANT4kr5ucOrytn+1tEP3RsQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770828681; c=relaxed/simple; bh=yhh2L0M0f2iEBhG2WaIT1K1aGPSS2NG3yjbS8XiHOZk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=UKnF/yGb5kKWh74ZhWnRDDHtEXPXb/sVEoTeCJTm/X7+KwslVaGc+SRjdSHDXBLMqK8rbEcVU+2F7T2mSGd9/YBMBDGsopYYtCiH3eZ/UvSliRCXB32ZZ0tdw6AjoktRYJKLXlNR+lyLFi3fKUK3BkEQsuZUT5uOmZjmlXWKPcU= 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=AFWUi9EI; 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="AFWUi9EI" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1770828679; 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=7xFvXHAT/zMR6zjSA8LwINVX0TELcD51yiOWZ67mo54=; b=AFWUi9EIcWKvuwuuf8CZNF5eOsDbL9ewayGnBIGqy5IS8EZWzUeAoRU/XQ3iSqO8YaiHuK zm8SqPT4eHv6ymCTHrdFSCV+OpMfRP0UPPoSFHfg2XNVYu/OF9lxvjM9JFEw4ssT2jN5uE QYI88126gA0ApphyBQ62aPkrK7Nt2oA= 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-644-Eh2aTJWBPDOU7fau04qHuQ-1; Wed, 11 Feb 2026 11:51:13 -0500 X-MC-Unique: Eh2aTJWBPDOU7fau04qHuQ-1 X-Mimecast-MFC-AGG-ID: Eh2aTJWBPDOU7fau04qHuQ_1770828671 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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 1BA9319560B3; Wed, 11 Feb 2026 16:51:10 +0000 (UTC) Received: from tpad.localdomain (unknown [10.96.133.3]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2A49919560B7; Wed, 11 Feb 2026 16:51:07 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id 974654084501B; Wed, 11 Feb 2026 13:50:45 -0300 (-03) Date: Wed, 11 Feb 2026 13:50:45 -0300 From: Marcelo Tosatti To: Michal Hocko , Vlastimil Babka 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. My bad, actually. Its only CONFIG_QPW on the current patchset. > > 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. > > Btw. have you measure the impact of preempt_disbale -> spinlock on hot > paths like SLUB sheeves? Nope, i have not. What is/are the standard benchmarks for SLUB/SLAB allocation ?