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Subject: Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and
 IO
To:     Johannes Weiner <hannes@cmpxchg.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Tejun Heo <tj@kernel.org>, Suren Baghdasaryan <surenb@google.com>,
        Daniel Drake <drake@endlessm.com>,
        Vinayak Menon <vinmenon@codeaurora.org>,
        Christopher Lameter <cl@linux.com>,
        Peter Enderborg <peter.enderborg@sony.com>,
        Shakeel Butt <shakeelb@google.com>,
        Mike Galbraith <efault@gmx.de>, 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 <rdunlap@infradead.org>
Message-ID: <6ff71c29-3b6a-4849-6f2a-3d829bbd43e2@infradead.org>
Date:   Tue, 28 Aug 2018 13:11:11 -0700
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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 <hannes@cmpxchg.org>
> +
> +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