| |
|
 |
|
 |
|
|
|
| |
|
|
xen-devel
Re: [Xen-devel] Credit scheduler
At 08:30 13/07/2007, Atsushi SAKAI wrote:
Hi, Prabha
pak333@xxxxxxxxxxx wrote:
[snip]
> > >Also, if the IO VM requests an IO, it will block and dom0 wakes up
> > >and gets scheduled to run to service the IO. Will it preempt the cpu
> > >intensive VM. If so why? Shouldn't the cpuintensiveV M get its
> > >quantum of time.
> > >Or does the IOVM get higher priority to preempt the cpu intensive
> > >VM. How does the scheduler pick which cpu to run dom0 on ( if all
> > >the vcpus running are cpu intensive)? If there is a mix of cpu-vcpus
> > >and Io-vcpus, which will be the victim
> >
> >
> > The whole idea of having separate queues for IO and CPU intensive VMs
> > (or processes in a normal kernel scenario) is to allow the
> > IO-intensive tasks to avoid waiting for the next time-slot when a
> > CPU-hogging VM/process is running [1]. The normal behaviour for the
> > scheduler is to determine dynamically if the current VM/process is IO
> > or CPU intensive.
> >
> > Unless Dom0 is used for doing some silly CPU-intensive task
> > (calculating PI with a million decimal points or compiling Xen +
> > Linux kernel, for example), it will most likely look to the scheduler
> > like a IO-intensive VM. So it will have the same priority as any
> > other IO-intensive VM (assuming Dom0 has equal scheduler parameters
> > as other guests, which I'm pretty sure is the default behaviour).
> >
> Does dom0 have a higher pritority than any CPU intensive VM
Easy way is to set higher weight to dom0.
(This makes get higher priority like I/O intensive domain for domain
dispatch)
If you want to set higher priority of Dom0 see follow patch.
(This is sample patch for boost Dom0 only not boost I/O intensive.)
http://lists.xensource.com/archives/html/xen-devel/2007-05/msg00529.html
Or just set CSCHED_PRI_TS_BOOST for domain0
in case dom0 priority is CSCHED_PRI_TS_UNDER.
> > If, like in your example, there are a number of processors busy with
> > CPU-intensive tasks, and others with IO-intensive tasks, the most
> > likely scenario is that any new IO-request will go be run on a
> > "previously CPU-intensive" CPU - but on the other hand, if you have a
> > lot of IO-intensive processing, there should be some processor(s)
> > that are "asleep" - unless all CPU's are busy running
CPU-intensive tasks...
> But will it preempt a CPU intensive vcpu if no cpu is available
[snip]
> >
> > [1] The idea being that if we process the IO-request that just
> > completed, we can set up another IO-request, and this will get better
> > IO-throughput than waiting a long time (relatively speaking 30ms is
> > an eternity to the processor).
> Don't understand what you mean here.
I guess Mats suggests to use AIO.
Well, sort of. I meant the idea behind waking an IO-intensive process
by pre-empting a CPU intensive process is that it improves the
overall IO throughput, because very often, once one IO request is
completed, another one will be requested. Hardware will take some
time to proces each request, at which time it's fine to run the
CPU-intensive process. If you prevent the IO intensive task from
running until the CPU-intensive task has exhausted it's time, it's
obviously going to take longer before the next IO-request is started,
and thus longer until it gets completed. It makes little difference
here if the APPLICATION is asynchronously or synchronously issuing
the IO-request (assuming that under asynchronous circumstances there
is a LIMITED amount of AIO queue - else it becomes a CPU-intensive
task building until it's issued all of the IO-requests and fall asleep).
--
Mats
Thanks
Atsushi SAKAI
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel
|
|
|
| |
|
Home