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From "Weldon Washburn" <weldon...@gmail.com>
Subject Re: [drlvm] finalizer design questions
Date Sun, 24 Dec 2006 13:23:00 GMT
On 12/23/06, Ivan Volosyuk <ivan.volosyuk@gmail.com> wrote:
>
> On 12/22/06, Weldon Washburn <weldonwjw@gmail.com> wrote:
> > On 12/22/06, Mikhail Fursov <mike.fursov@gmail.com> wrote:
> > >
> > > Weldon,
> > > AFAIR without WBS it's an easy to write a test(we had such tests) that
> > > will
> > > work smoothly on SUN or BEA but fails on Harmony.
> > > Is "run any app RI is able to run" reason enough?
> >
> >
> > Yes indeed this is reason enough for this stage of Harmony VM
> development.
> > Taken to the limit, "run any app RI is able to run" means cloning the
> RI.
> > At some point in the future we will need to revisit the above rule but
> its
> > good nuff for now.
>
> BTW, the work balancing system was introduced to workaround missing
> high priority threads in VM. IMHO, a high priority finalizer thread
> can do the job.


Very interesting.  Please tell me if the following is correct.  Without WBS,
finalizing objects falls further and further behind because finalization
thread(s) are unable to grab enough of the CPU(s) to keep up.  Instead of
increasing the priority of the finalization thread(s), WBS takes the
approach of increasing the number of finalization threads.  The net effect
is to increase the rate of finalization by diluting the OS ready queue.

Does the following alternative design make sense?  Assume the OS/VM porting
layer allows the VM to change an OS thread's priority appropriately.  During
VM boot, query the OS to determine the number of CPUs in the box and create
one finalizer thread for each CPU.  Never create additional finalizer
threads.  Boost the priority of the finalizer threads above the level of
Java app threads (but probably below real time priority.)  Note that all of
this is orthogonal to "native" vs. "java" finalizer threads.

--
> Ivan
>
> >
> > On 12/22/06, Weldon Washburn <weldonwjw@gmail.com> wrote:
> > > >
> > > > The existing VM finalizer system has something called a Work
> Balancing
> > > > System.  It would be good to know the motivation for this
> feature.  If
> > > > this
> > > > feature was built for specific workloads, please tell us which ones.
> > > >   Thanks
>



-- 
Weldon Washburn
Intel Enterprise Solutions Software Division

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