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Received: from static-50-53-52-16.bvtn.or.frontiernet.net ([50.53.52.16] helo=midway.dunlab) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fukKZ-0004o0-DL; Tue, 28 Aug 2018 20:11:15 +0000 Subject: Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO To: Johannes Weiner , Ingo Molnar , Peter Zijlstra , Andrew Morton , Linus Torvalds Cc: Tejun Heo , Suren Baghdasaryan , Daniel Drake , Vinayak Menon , Christopher Lameter , Peter Enderborg , Shakeel Butt , Mike Galbraith , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com References: <20180828172258.3185-1-hannes@cmpxchg.org> <20180828172258.3185-9-hannes@cmpxchg.org> From: Randy Dunlap Message-ID: <6ff71c29-3b6a-4849-6f2a-3d829bbd43e2@infradead.org> Date: Tue, 28 Aug 2018 13:11:11 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180828172258.3185-9-hannes@cmpxchg.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/28/2018 10:22 AM, Johannes Weiner wrote: > diff --git a/Documentation/accounting/psi.txt b/Documentation/accounting/psi.txt > new file mode 100644 > index 000000000000..51e7ef14142e > --- /dev/null > +++ b/Documentation/accounting/psi.txt > @@ -0,0 +1,64 @@ > +================================ > +PSI - Pressure Stall Information > +================================ > + > +:Date: April, 2018 > +:Author: Johannes Weiner > + > +When CPU, memory or IO devices are contended, workloads experience > +latency spikes, throughput losses, and run the risk of OOM kills. > + > +Without an accurate measure of such contention, users are forced to > +either play it safe and under-utilize their hardware resources, or > +roll the dice and frequently suffer the disruptions resulting from > +excessive overcommit. > + > +The psi feature identifies and quantifies the disruptions caused by > +such resource crunches and the time impact it has on complex workloads > +or even entire systems. > + > +Having an accurate measure of productivity losses caused by resource > +scarcity aids users in sizing workloads to hardware--or provisioning > +hardware according to workload demand. > + > +As psi aggregates this information in realtime, systems can be managed > +dynamically using techniques such as load shedding, migrating jobs to > +other systems or data centers, or strategically pausing or killing low > +priority or restartable batch jobs. > + > +This allows maximizing hardware utilization without sacrificing > +workload health or risking major disruptions such as OOM kills. > + > +Pressure interface > +================== > + > +Pressure information for each resource is exported through the > +respective file in /proc/pressure/ -- cpu, memory, and io. > + Hi, > +In both cases, the format for CPU is as such: I don't see what "In both cases" refers to here. It seems that you could just remove it. > + > +some avg10=0.00 avg60=0.00 avg300=0.00 total=0 > + > +and for memory and IO: > + > +some avg10=0.00 avg60=0.00 avg300=0.00 total=0 > +full avg10=0.00 avg60=0.00 avg300=0.00 total=0 > + > +The "some" line indicates the share of time in which at least some > +tasks are stalled on a given resource. -- ~Randy