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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 1fulZ6-0005Ay-3U; Tue, 28 Aug 2018 21:30:20 +0000 Subject: Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO To: Johannes Weiner Cc: Ingo Molnar , Peter Zijlstra , Andrew Morton , Linus Torvalds , 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> <6ff71c29-3b6a-4849-6f2a-3d829bbd43e2@infradead.org> <20180828205625.GA14030@cmpxchg.org> From: Randy Dunlap Message-ID: Date: Tue, 28 Aug 2018 14:30:17 -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: <20180828205625.GA14030@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 01:56 PM, Johannes Weiner wrote: > On Tue, Aug 28, 2018 at 01:11:11PM -0700, Randy Dunlap wrote: >> 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. > > You're right, that must be a left-over from when I described CPU > separately; "both cases" referred to memory and IO which have > identical formats. It needs to be removed: > > diff --git a/Documentation/accounting/psi.txt b/Documentation/accounting/psi.txt > index e051810d5127..b8ca28b60215 100644 > --- a/Documentation/accounting/psi.txt > +++ b/Documentation/accounting/psi.txt > @@ -35,7 +35,7 @@ Pressure interface > Pressure information for each resource is exported through the > respective file in /proc/pressure/ -- cpu, memory, and io. > > -In both cases, the format for CPU is as such: > +The format for CPU is as such: > > some avg10=0.00 avg60=0.00 avg300=0.00 total=0 OK. However, after reading patch 9/9, I thought that the "both cases" could possibly mean the files in /proc/pressure/ and the files in cgroup ({cpu,io,memory}.pressure). -- ~Randy