Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

Randy Dunlap
2018-08-28T20:11:11Z

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