[LITMUS^RT] Question about the scheduling overhead of GSN-EDF scheduler in LITMUS

[Meng Xu]

Hi Bjorn,

2015-10-13 4:54 GMT-04:00 Björn Brandenburg <bbb at mpi-sws.org>:

>
> > On 11 Oct 2015, at 16:57, Meng Xu <xumengpanda at gmail.com> wrote:
> >
> >
> > ​I actually have one question about this:
> > Why the background cache-intensive task will affect the scheduling
> overhead?
> > Is it because the ready_queue data may be polluted by the background
> tasks so that it will take longer time to take one task from ready_queue
> and therefore increases the critical section?
> > I'm not sure if there is any other reason why the background tasks can
> increase the scheduling overhead. ​
>
> Hi Meng,
>
> by running a cache-thrashing background workload, the cost of a memory
> accesses increases significantly. Basically, the rate of cache misses
> increases (scheduler data structures are more likely to be evicted between
> invocations of the scheduler) and any cache miss becomes much more
> expensive (because the memory controller is under heavy load). Basically,
> to approximate near-worst-case performance, you need to create lots of
> potential for interference at all shared hardware resources.
>

​Thank you so much for your help and time in answering these questions!
They are really helpful!

Best regards,

Meng​




-----------
Meng Xu
PhD Student in Computer and Information Science
University of Pennsylvania
http://www.cis.upenn.edu/~mengxu/
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