From mboxrd@z Thu Jan 1 00:00:00 1970 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 91EC3C77B73 for ; Wed, 19 Apr 2023 11:20:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232938AbjDSLUl (ORCPT ); Wed, 19 Apr 2023 07:20:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48626 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232296AbjDSLUe (ORCPT ); Wed, 19 Apr 2023 07:20:34 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5C16415445 for ; Wed, 19 Apr 2023 04:19:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1681903132; 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=W4Ui46Ta0P2TP7Rwzqo3VE9KCOz5jOSMpJOW/7SNy88=; b=i2t8YS6+0TK0+y7y7kqLlmO37JvPTI5x/QLEUEVMXYTJ8LEEVBJPTZ6irOyfki1BBahmIo tsYPyxLD/UsP06in4x9cEk2fbWwYJd37xceNhi/F8hCXosi/DcBSl5keYBh+wUIpr9AEWm PpkbmXmu8kt16qgfceYXIiu88NgeM/Q= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-595-FiNbAEzrNVuVLWm7VGa_LA-1; Wed, 19 Apr 2023 07:18:49 -0400 X-MC-Unique: FiNbAEzrNVuVLWm7VGa_LA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 981FD811E7D; Wed, 19 Apr 2023 11:18:48 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 61EC340BC799; Wed, 19 Apr 2023 11:18:48 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id 04C00401CA8CB; Wed, 19 Apr 2023 08:15:56 -0300 (-03) Date: Wed, 19 Apr 2023 08:15:56 -0300 From: Marcelo Tosatti To: Andrew Morton , Andrew Theurer Cc: Christoph Lameter , Aaron Tomlin , Frederic Weisbecker , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Russell King , Huacai Chen , Heiko Carstens , x86@kernel.org, Vlastimil Babka , Michal Hocko Subject: Re: [PATCH v7 00/13] fold per-CPU vmstats remotely Message-ID: References: <20230320180332.102837832@redhat.com> <20230418150200.027528c155853fea8e4f58b2@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 19, 2023 at 08:14:09AM -0300, Marcelo Tosatti wrote: > On Tue, Apr 18, 2023 at 03:02:00PM -0700, Andrew Morton wrote: > > On Mon, 20 Mar 2023 15:03:32 -0300 Marcelo Tosatti wrote: > > > > > This patch series addresses the following two problems: > > > > > > 1. A customer provided evidence indicating that a process > > > was stalled in direct reclaim: > > > > > > ... > > > > > > 2. With a task that busy loops on a given CPU, > > > the kworker interruption to execute vmstat_update > > > is undesired and may exceed latency thresholds > > > for certain applications. > > > > > > > I don't think I'll be sending this upstream in the next merge window. > > Because it isn't clear that the added complexity in vmstat handling is > > justified. > > From my POV this is an incorrect statement (that the complexity in > vmstat handling is not justified). > > Andrew, this is the 3rd attempt to fix this problem: > > First try: https://lore.kernel.org/lkml/20220127173037.318440631@fedora.localdomain/ > > Second try: https://patchew.org/linux/20230105125218.031928326@redhat.com/ > > Third try: syncing vmstats remotely from vmstat_shepherd (this > patchset). > > And also, can you please explain: what is so complicated about the > vmstat handling? cmpxchg has been around and is used all over the > kernel, and nobody considers "excessively complicated". > > > - Michal's request for more clarity on the end-user requirements > > seems reasonable. > > And i explained to Michal in great detail where the end-user > requirements come from. For virtualized workloads, there are two > types of use-cases: > > 1) For example, for the MAC scheduler processing must occur every 1ms, > and a certain amount of computation takes place (and must finish before > the next 1ms timeframe). A > 50us latency spike as observed by cyclictest > is considered a "failure". > > I showed him a 7us trace caused by, and explained that will extend to > > 50us in the case of virtualized vCPU. > > 2) PLCs. These workloads will also suffer > 50us latency spikes > which is undesirable. > > Can you please explain what additional clarity is required? > > RH's performance team, for example, has been performing packet > latency tests and waiting for this issue to be fixed for about 2 > years now. > > Andrew Theurer, can you please explain what problem is the vmstat_work > interruption causing in your testing? +CC Andrew.