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[2603:800c:1a02:1bae:e24f:43ff:fee6:449f]) by smtp.gmail.com with ESMTPSA id z16sm5017479pgi.89.2022.01.14.08.30.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 14 Jan 2022 08:30:36 -0800 (PST) Date: Fri, 14 Jan 2022 06:30:34 -1000 From: Tejun Heo To: Peter Zijlstra Cc: Daniel Jordan , Alexander Duyck , Alex Williamson , Andrew Morton , Ben Segall , Cornelia Huck , Dan Williams , Dave Hansen , Dietmar Eggemann , Herbert Xu , Ingo Molnar , Jason Gunthorpe , Johannes Weiner , Josh Triplett , Michal Hocko , Nico Pache , Pasha Tatashin , Steffen Klassert , Steve Sistare , Tim Chen , Vincent Guittot , linux-mm@kvack.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org Subject: Re: [RFC 15/16] sched/fair: Account kthread runtime debt for CFS bandwidth Message-ID: References: <20220106004656.126790-1-daniel.m.jordan@oracle.com> <20220106004656.126790-16-daniel.m.jordan@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: AAADDA0013 X-Stat-Signature: if67cq1mngxg735m3hukzt4d3n64q6br Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=a9EtpM5f; spf=pass (imf15.hostedemail.com: domain of htejun@gmail.com designates 209.85.216.47 as permitted sender) smtp.mailfrom=htejun@gmail.com; dmarc=fail reason="SPF not aligned (relaxed), DKIM not aligned (relaxed)" header.from=kernel.org (policy=none) X-HE-Tag: 1642177837-936927 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: Hello, On Fri, Jan 14, 2022 at 10:31:55AM +0100, Peter Zijlstra wrote: > So part of the problem I have with this is that these external things > can consume all the bandwidth and basically indefinitely starve the > group. > > This is doulby so if you're going to account things like softirq network > processing. So, anything which is accounted this way should slow down / stall the originator so that backcharges can't run away. In many cases, these connections are already there - e.g. if you keep charging socket rx buffers to a cgroup, the processes in the cgroup will slow down and the backpressure on the network socket will slow down the incoming packets. Sometimes, the backpressure propagation needs to be added explicitly - e.g. filesystem metadata writes can run away because something can keeping on issuing metadata updates without getting throttled neither on memory or io side. So, for situations like that, we need to add an explicit mechanism to throttle the originator asynchronously. Thanks. -- tejun