Re: [Xen-devel] [PATCH] credit: Change default timeslice to 5ms

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On gio, 2014-03-06 at 12:04 +0000, George Dunlap wrote:
> On 03/05/2014 05:18 PM, David Vrabel wrote:
> > On 05/03/14 16:29, George Dunlap wrote:
> >> --- a/xen/common/sched_credit.c
> >> +++ b/xen/common/sched_credit.c
> >> @@ -29,9 +29,9 @@
> >>    * Basic constants
> >>    */
> >>   #define CSCHED_DEFAULT_WEIGHT       256
> >> -#define CSCHED_TICKS_PER_TSLICE     3
> >> -/* Default timeslice: 30ms */
> >> -#define CSCHED_DEFAULT_TSLICE_MS    30
> >> +#define CSCHED_TICKS_PER_TSLICE     1
> > The TICKS_PER_TSLICE change doubles the tick rate.  Is this intentional?
> >   It's not mentioned in the commit message.
> 
> Hmm -- actually, I just realized that Marcus' test was done with 3 ticks 
> per timeslice, so "5ms / 1 tick" has *not* been validated. And this is 
> actually important, because the main purpose of the ticks is to give the 
> scheduler an opportunity to switch VMs out of "BOOST" priority and into 
> "UNDER" priority.  Reducing the ticks per timeslice changes that 
> dynamic, and would need to be tested separately.
> 
Which is even higher tick frequency, isn't it? Anyway, you're right, we
should go for the tested solution.

> Also, I just discovered a rather pathological case in general that seems 
> to be in the scheduler, so for the time being let me retract this while 
> I figure that out.
> 
Care to share some more details about this?

Regards,
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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