Re: [LSF/MM ATTEND] Expanding OS noise suppression

[Christoph Lameter <cl@linux.com>]

Sorry the list address was not correct

On Mon, 24 Nov 2014, Christoph Lameter wrote:

> Recently a lot of work has been done in the kernel to be able to keep OS
> threads off low latency cores with the NOHZ work mainly pushed by Frederic
> Weisbecker (also also Paul McKenney modifying RCU for that purpose). With
> that approach we may now reduce the timer tick to a frequency of 1 per
> second. The result of that work is now available in Redhat 7.
>
> I have recently submitted work on the vmstat kworkers that makes the
> kworkers run on demand with a shepherd worker checking from a non low
> latency processor if there is actual work to be done on a processor in low
> latency mode. If not then the kworker requests can be avoided and
> therefore activities on that processor are reduced. This approach can be
> extended to cover other necessary activities on low latency cores.
>
> There is other work in progress to limit unbound kworker threads to no
> NOHZ processors. Also more work is in flight to work on various issues in
> the scheduler to enable us to hold off the timer tick for more than one
> second.
>
> There are numerous other issues that can impact on a low latency core from
> the memory management system. I would like to discuss ways that we can
> further ensure that OS activities do not impact latency critical threads
> running on special nohz cores.
>
> This may cover:
>  - minor and major faults and how to suppress them effectively.
>  - Processor cache impacts by sibling threads.
>  - IPIs
>  - Control over various subsystem specific per cpu threads.
>  - Control impacts of scans for defragmentation and THP on these cores.
>
> There was a recent discussion on the subject matter on lkml that mentions
> a number of the pending issues in this area:
>
> https://lkml.org/lkml/2014/11/11/679
> https://lkml.org/lkml/2014/10/31/364
>
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