Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 47090C433F5 for ; Tue, 14 Dec 2021 12:26:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233905AbhLNM0W (ORCPT ); Tue, 14 Dec 2021 07:26:22 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:25501 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231744AbhLNM0V (ORCPT ); Tue, 14 Dec 2021 07:26:21 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1639484781; 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=fNWLhg1ntWwp5Ppu09h0Eh4UGAn0KphaoLRSOYk8nM8=; b=eVtRvroIUm25LBT5UegrjVYI11halhJU8UXUpLdjV0uklb+I+Do8iqOTfuLWjYiLpDrPQx MNYCStL2u3/F3r3jNJBiT5J3Uh2/daMKh/YXzAQjfMPaNViRW4NQSa8vznM2V3Id6ThpyR bBKPel6cRP3zoF3xQ3nX0fdCy8nngMM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-540-BMYZV-O3O2KuLxy71sdZRg-1; Tue, 14 Dec 2021 07:26:18 -0500 X-MC-Unique: BMYZV-O3O2KuLxy71sdZRg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 63D3B192CC40; Tue, 14 Dec 2021 12:26:16 +0000 (UTC) Received: from fuller.cnet (ovpn-112-3.gru2.redhat.com [10.97.112.3]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 38EEE5E26D; Tue, 14 Dec 2021 12:26:01 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id 506EA416D862; Tue, 14 Dec 2021 09:25:58 -0300 (-03) Date: Tue, 14 Dec 2021 09:25:58 -0300 From: Marcelo Tosatti To: Christoph Lameter Cc: Mel Gorman , Thomas Gleixner , Frederic Weisbecker , Christoph Lameter , Nicolas Saenz Julienne , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, peterz@infradead.org, nilal@redhat.com, linux-rt-users@vger.kernel.org, vbabka@suse.cz, ppandit@redhat.com Subject: Re: [PATCH v2 3/3] mm/page_alloc: Remotely drain per-cpu lists Message-ID: <20211214122558.GB57271@fuller.cnet> References: <20211103170512.2745765-1-nsaenzju@redhat.com> <20211103170512.2745765-4-nsaenzju@redhat.com> <20211203141306.GG3301@suse.de> <20211209174535.GA70283@fuller.cnet> <20211210105549.GJ3301@suse.de> <20211214105823.GA53878@fuller.cnet> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 14, 2021 at 12:42:58PM +0100, Christoph Lameter wrote: > On Tue, 14 Dec 2021, Marcelo Tosatti wrote: > > > > downside is that there will be a performance penalty if an application > > > running on a NOHZ_FULL CPU is page allocator intensive for whatever > > > reason. However, I guess this is unlikely because if there was a lot > > > of kernel activity for a NOHZ_FULL CPU, the vmstat shepherd would also > > > cause interference. > > > > Yes, it does, and its being fixed: > > > > https://lkml.org/lkml/2021/12/8/663 > > > > Honestly i am not sure whether the association between a nohz_full CPU > > and "should be mostly in userspace" is desired. The RCU solution > > would be more generic. As Nicolas mentioned, for the usecases in > > questions, either solution is OK. > > > > Thomas, Frederic, Christoph, do you have any opinion on this ? > > Applications running would ideally have no performance penalty and there > is no issue with kernel activity unless the application is in its special > low latency loop. NOHZ is currently only activated after spinning in that > loop for 2 seconds or so. Would be best to be able to trigger that > manually somehow. Can add a task isolation feature to do that. > And I would prefer to be able to run the whole system as > NOHZ and have the ability to selectively enable the quiet mode if a > process requires it for its processing. IIRC Frederic has been working on that. Thanks.