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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 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 755D54001C X-Stat-Signature: ie4ige91k8dp1a8q8fat5f84m6r3secb X-HE-Tag: 1681903133-142016 X-HE-Meta: U2FsdGVkX18qXgrM7pE+DW6Gdnzu1rkNp0y+PsmgOaZHj8K71Nr+A9si9Vj96aVlf8nck1Rj38s1h20MjkDqplVWbxprISTtKdovizRdgNOfSsMyRG7CKSg+NkKahmv5oVJHHHYKk4bUJe/ok0ijAKQ5wMFActBf4XMoZVIfJ16LDnQCsiF1mb3c5+LMSOmaKEPlE98vIBCkJPaaUYMIwt9TitckjOa/KtvrSTiGO7cY/DmmBUljfGWFkPQoIVOMT3s/1xwpFFDT18svHCK3HwvxbWtKdi7nEAZ+smA+FIW6EkxFQ4cARCzdo3jOCSb+aHXgyHa2j04efRFiIxYRtgHGbleVYWEJQ6iOWKtsovbCNcPdlKEo4k9Z7r0sD2Gw66ZTWeZwFj9MatNvYr9XO90aARtGaabr2PzIJci8K9qLO4+qSkR9z8+gXM13jr88yBkDwB2zkzdvOs4b9hixQDuioLwgzhiW3R8K6aH5J1rVl8wJx+xxTybttLDVUfbrtvUg6BpQe2EEGG7zZvwCNwhWvy1vtk8tOLo8A3pvahsrQxJI9cnvF1h1OPXRcGZ5fsi4PvxfCfB/NgNXilQp8A8eVtuWa5eGL5DfJX+gieJDt2UO+/EHoc/ococzutexh34O2dWGjtFB0OMD8x3rSbb2xL5BDNBGxlHv91dJdHw2SQ5J9jGU7JlPH/LXmYzo8Sf5CR0B7H88VAtEhC+c+th05FR+XuemvCP+fpRxiLDmHuiVdEf0ed2Fev5uknomAAdX5vx9f48IL72DhJ+DLcoHgRUoT98iqWvUc42e5WS+2uBWcCWHIIaJtbjgkLNeJHb46XuyxUdmw/bllbDNf6BPLBM4n1jr5moKeczGk6hRzfTDd/q9KPRJeE2I3gb/QIUcqWRRE5/jDe6X9jsxWBK/pQYMZIDYFS2wULaQ+LvmABpRJ4Yb8OcqW+EeAmzWQUjvB2SeqN/atsXCvmF u3cwJ1oC KLOstjHBzSHQ+4xVu+cueiLaTdpOyOK1OzK4rtd/q94LOVDVqUiSZxe0V80DPATEJgK+JiFFrVt0YKat6M30NlwG6jXPr2DeN4QYPkTbQbDyGYVzGxNanztcGs7aepDdM2R8cdnyJWfZy91i8geA1tLWvvtDxV93UEuaOkbTFurywGBjHIQwvEQb20bSAugz2NRxzOlkqLyAn6KtzaaLo0aWrbQZ6D+yLE0Qa54wB3+Up/ULGEdBaEaZk96SOFq/tOABPvV9dWH8Lmxe7WxsM8LKAf93pbnH/AyyRhDwLKVz3DWb1EjvYSthvfHUCwHA58RH9 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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.