Re: [Xen-devel] Xen on ARM IRQ latency and scheduler overhead

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Mon, 2017-02-20 at 11:04 +0000, George Dunlap wrote:
> On 18/02/17 00:41, Stefano Stabellini wrote:
> > 
> > On Fri, 17 Feb 2017, Dario Faggioli wrote:  
> > >           cyclictest 1us  cyclictest 1ms  cyclictest
> > > 100ms                     
> > > (cycles)  Credit1 Credit2 Credit1 Cred
> > > it2       Credit1 Credit2         
> > > wakeup-avg        2429    2035    1980    1633    
> > > 2535      1979            
> > > wakeup-max        14577   113682  15153   203136  
> > > 12285     115164          
> > 
> > I am not that familiar with the x86 side of things, but the 113682
> > and
> > 203136 look worrisome, especially considering that credit1 doesn't
> > have
> > them.
> 
> Dario,
> 
> Do you reckon those 'MAX' values could be the load balancer running
> (both for credit1 and credit2)?
> 
If they were max-es of do_schedule, that would have been my first
guess. But not in this case, as the load balancer is never called
during wakeup (neither in Credit nor Credit2).

But I'm curious about what happen, and am going to investigate that. It
should not be too hard has: 1) looks reproducible on my (x86) testbox
that I have here; 2) since it's x86 I have tracing! :-P

Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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