On Monday, 22 May 2017 16:03:53 UTC+3, Wojciech Kudla wrote:
>
> There's lots of work being scheduled on even isolated cpus. If you are not 
> running a tickless kernel, you should see around 1000 local timer 
> interrupts per second (by default). You will also see soft irqs (if you 
> haven't affinitized them with some housekeeping cpu), non maskable 
> interrupts/machine check errors, work queue tasks, etc. 
> As for rcu, even with offloading you will see the isolated cores 
> performing work required to schedule the callbacks on the offloaded cpus. 
> You can solve that by switching to rcu callback polling, but my point here 
> is, there's a number of different types of tasks that will run on isolated 
> cpus.
>

Kernel can run work queue tasks on isolated cores quiet often, can observe 
them via:

# perf record -C 1 -e  workqueue:workqueue_execute_start -e 
workqueue:workqueue_execute_end  -o wrk_start_$(date "+%Y-%m-%d_%H%M")  -- 
sleep 300

Sometimes things like cursor blink or EDAC can be avoided/reduced.

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