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Tue, 28 Aug 2018 13:56:26 -0700 (PDT) Date: Tue, 28 Aug 2018 16:56:25 -0400 From: Johannes Weiner To: Randy Dunlap 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 Subject: Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO Message-ID: <20180828205625.GA14030@cmpxchg.org> References: <20180828172258.3185-1-hannes@cmpxchg.org> <20180828172258.3185-9-hannes@cmpxchg.org> <6ff71c29-3b6a-4849-6f2a-3d829bbd43e2@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6ff71c29-3b6a-4849-6f2a-3d829bbd43e2@infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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