Re: [Xen-devel] Credit scheduler

[Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx>]

Hi Prabha

Please check do_softirq in assembler.
for x86 
call do_softirq 
is in.

And usually do_softirq is executed at the end of system call.

Thanks
Atsushi SAKAI



pak333@xxxxxxxxxxx wrote:

> Thanks for the explanation, i am not sure i understood it correctly.
> 
> 
> when does softirq get set. So when softirq is set a processor enters the 
> scheduler every 3 micro secs? where in the source code is this handled. 
> please could you send me some pointers
> 
> thanks
> -Prabha
> 
> 
> 
> 
> -------------- Original message -------------- 
> From: Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx> 
> 
> > Hi,　Prabha 
> > 
> > 　30msec is the maximum time slice. 
> > And I guess your 3 microsecond is the response after 
> > SCHEDULE_SOFTIRQ is set. 
> > As you know, 
> > If SCHEDULE_SOFTIRQ is set, 
> > it waits softirq calls schedule(). (this time interval is 3microsec) 
> > 
> > And I/O intensive has higher priority than CPU intensive. 
> > So I/O intensive job is first dispatched domain in runq. 
> > This is because latency improvement for I/O intensive guest. 
> > 
> > So your behavior is not strange. 
> > 
> > Thanks 
> > Atsushi SAKAI 
> > 
> > 
> > pak333@xxxxxxxxxxx wrote: 
> > 
> > > Hi 
> > > 
> > > I have noticed that VMs are typically spending 3 microsecs or less before 
> > > they 
> > are being prempted. I thought that the credit schduler time slice was 30 
> > ms. I 
> > have 4 VMs running and they are all cpu intensive except for 1 (which is IO 
> > intensive) but having a VM spend max 3 micro secs before being kicked out 
> > seems 
> > strange. 
> > > 
> > > Is there something else going on that i am not aware of. Is the time 
> > > slice 
> > really 30 millisecs? I am using default parameters of the credit scheduler. 
> > > 
> > > Thanks 
> > > -Prabha 
> > 
> > 



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