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 F4121C433EF for ; Tue, 7 Dec 2021 16:35:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233781AbhLGQj0 (ORCPT ); Tue, 7 Dec 2021 11:39:26 -0500 Received: from serv108.segi.ulg.ac.be ([139.165.32.111]:53530 "EHLO serv108.segi.ulg.ac.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229709AbhLGQjW (ORCPT ); Tue, 7 Dec 2021 11:39:22 -0500 Received: from mbx12-zne.ulg.ac.be (serv470.segi.ulg.ac.be [139.165.32.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by serv108.segi.ulg.ac.be (Postfix) with ESMTPS id 92BFB200F81B; Tue, 7 Dec 2021 17:35:49 +0100 (CET) DKIM-Filter: OpenDKIM Filter v2.11.0 serv108.segi.ulg.ac.be 92BFB200F81B DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=uliege.be; s=ulg20190529; t=1638894949; bh=kCTMHmqBI/ompkL5Jcr5fy8SFmAAf7AcqDUt71hh6iI=; h=Date:From:Reply-To:To:Cc:In-Reply-To:References:Subject:From; b=QUcrWDBRVdeof0Tamz/6wWdRNkuTRM+2DV/WAYNedOIXmSo79HDP/JPcfchkIR7nH ZI/h4Zss710v8QwUCcq7XKzntGrurML9s5akt6k0eBR1qa6r/eJl0MWk1zNo9N7hl4 kgJnhHDKeiSExcM5AXRgsGMveB6cS5kAnbtHOoXEkU8pq/25Ab277MmwLfDTKodPy8 KNe5oDgRQqo06gfyuTf+bjYZuVTTSqxAtT4c9Bc01zTV9l5mTy25J34SR9aQGWlwhZ u7F0FLeq3MJWiRqH4hOT6q522Euxy2BMtIQACHUzQlhTju/Od+J66YROlmFtqlNYXi BPAXeZzpRHS5Q== Received: from localhost (localhost [127.0.0.1]) by mbx12-zne.ulg.ac.be (Postfix) with ESMTP id 858C260225373; Tue, 7 Dec 2021 17:35:49 +0100 (CET) Received: from mbx12-zne.ulg.ac.be ([127.0.0.1]) by localhost (mbx12-zne.ulg.ac.be [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id yUnivlg35vCE; Tue, 7 Dec 2021 17:35:49 +0100 (CET) Received: from mbx12-zne.ulg.ac.be (mbx12-zne.ulg.ac.be [139.165.32.199]) by mbx12-zne.ulg.ac.be (Postfix) with ESMTP id 688BF6008D79D; Tue, 7 Dec 2021 17:35:49 +0100 (CET) Date: Tue, 7 Dec 2021 17:35:49 +0100 (CET) From: Justin Iurman Reply-To: Justin Iurman To: Jakub Kicinski Cc: netdev@vger.kernel.org, davem@davemloft.net, dsahern@kernel.org, yoshfuji@linux-ipv6.org, linux-mm@kvack.org, cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo kim , akpm@linux-foundation.org, vbabka@suse.cz Message-ID: <1045511371.220520131.1638894949373.JavaMail.zimbra@uliege.be> In-Reply-To: <20211207075037.6cda8832@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> References: <20211206211758.19057-1-justin.iurman@uliege.be> <20211206211758.19057-3-justin.iurman@uliege.be> <20211206161625.55a112bb@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <262812089.220024115.1638878044162.JavaMail.zimbra@uliege.be> <20211207075037.6cda8832@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Subject: Re: [RFC net-next 2/2] ipv6: ioam: Support for Buffer occupancy data field MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [81.240.24.148] X-Mailer: Zimbra 8.8.15_GA_4018 (ZimbraWebClient - FF94 (Linux)/8.8.15_GA_4026) Thread-Topic: ipv6: ioam: Support for Buffer occupancy data field Thread-Index: Avbm4/re1gCK09gzGU7eD5s9hVgDug== Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Dec 7, 2021, at 4:50 PM, Jakub Kicinski kuba@kernel.org wrote: > On Tue, 7 Dec 2021 12:54:04 +0100 (CET) Justin Iurman wrote: >> >> The function kmem_cache_size is used to retrieve the size of a slab >> >> object. Note that it returns the "object_size" field, not the "size" >> >> field. If needed, a new function (e.g., kmem_cache_full_size) could be >> >> added to return the "size" field. To match the definition from the >> >> draft, the number of bytes is computed as follows: >> >> >> >> slabinfo.active_objs * size >> > >> > Implementing the standard is one thing but how useful is this >> > in practice? >> >> IMHO, very useful. To be honest, if I were to implement only a few data >> fields, these two would be both included. Take the example of CLT [1] >> where the queue length data field is used to detect low-level issues >> from inside a L5-7 distributed tracing tool. And this is just one >> example among many others. The queue length data field is very specific >> to TX queues, but we could also use the buffer occupancy data field to >> detect more global loads on a node. Actually, the goal for operators >> running their IOAM domain is to quickly detect a problem along a path >> and react accordingly (human or automatic action). For example, if you >> monitor TX queues along a path and detect an increasing queue on a >> router, you could choose to, e.g., rebalance its queues. With the >> buffer occupancy, you could detect high-loaded nodes in general and, >> e.g., rebalance traffic to another branch. Again, this is just one >> example among others. Apart from more accurate ECMPs, you could for >> instance deploy a smart (micro)service selection based on different >> metrics, etc. >> >> [1] https://github.com/Advanced-Observability/cross-layer-telemetry > > Ack, my question was more about whether the metric as implemented Oh, sorry about that. > provides the best signal. Since the slab cache scales dynamically > (AFAIU) it's not really a big deal if it's full as long as there's > memory available on the system. Well, I got the same understanding as you. However, we do not provide a value meaning "X percent used" just because it wouldn't make much sense, as you pointed out. So I think it is sound to have the current value, even if it's a quite dynamic one. Indeed, what's important here is to know how many bytes are used and this is exactly what it does. If a node is under heavy load, the value would be hell high. The operator could define a threshold for each node resp. and detect abnormal values. We probably want the metadata included for accuracy as well (e.g., kmem_cache_size vs new function kmem_cache_full_size).