Re: [Xen-devel] Scheduling of I/O domains

["G. Milos" <gm281@xxxxxxxxxxxxxxxx>]

The patch you sent probably does work, but most of the code responsible 
for waking up got pushed into specific schedulers (i.e. it is not in 
schedule.c but in sched_bvt.c, sched_rrobin.c etc). I have replaced the 
"min <= now" bit by what BVT research paper suggests and only 
0.7% difference was observed in the dd test. It would be nice if you could 
run the dd test on your machine after updating your xen code.
Also, yesterday I checked in a working version of the warping mechanism 
(anybody wants to test it, and report bugs to me?). If we run the 
IO-domains warped the difference in dd will probably be even smaller.
> > The proper fix should be a call into the scheduler if a task unblocks,
> > which shouldn't be too hard to add.
> I found a simple way of doing this. In schedule.c/domain_wake(), I changed 
> the following code slightly:
>        if ( is_idle_task(curr) || (min_time <= now) )
>            cpu_raise_softirq(cpu, SCHEDULE_SOFTIRQ);
> This code causes the scheduler to be run if the current task is the idle 
> task, or if the current task has already used up its time slice. I changed 
> this to:
>        if ( is_idle_task(curr) || (min_time <= now)
>                 || IS_CAPABLE_PHYSDEV(d) )
>            cpu_raise_softirq(cpu, SCHEDULE_SOFTIRQ);
>
> This causes the scheduler also to be run if the domain we are waking up is a 
> device domain.
> The stock BVT scheduling code seems to take care of the rest. Since the 
> device domain tends to run relatively rarely, its virtual time is smaller, 
> which causes the BVT algorithm to switch to it right away.
> This changes the result of my little 'dd' test to be much closer to nominal:
>
> time dd if=/dev/hda5 bs=1024k count=11 of=/dev/null
>
> takes 1.96s with nothing else running.
>
> takes 2.1s with a cpu intensive domain running concurrently
>
> took over 8s without this change.
>
> Maybe not perfect, but way better.
>
>
> Rob Gardner
> HP
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