[Haifux] [HAIFUX LECTURE] OFFSCHED - Offline Scheduler by Raz Ben-Yehuda

Orna Agmon Ben-Yehuda ladypine at gmail.com
Sun Jan 3 10:25:48 MSK 2010

On Monday, January 4th (TOMORROW) at 18:30, Haifux will gather to open
the year 2010 and hear Raz Ben-Yehuda (Open University Masters
Student) talk about the

          Offline Scheduler


OFFSCHED is a platform aimed to assign an assignment to an offloaded
processor. An offloaded processor is a processor that is hot
un-plugged from the operating system. In today's computer world, we
find that most processors have several embedded cores and
hyper-threading. Most programmers do not really use these powerful
features and let the operating system do the work. At most, a
programmer will bound an application to a certain processor or assign
an interrupt to a different processor.

At the end, we get a system busy in maintaining tasks across
processors, balancing interrupts, flushing TLBs and DTLBs using atomic
operations even when not needed and worst of all, spin locks across
processors in vein; and the more processors the merrier. I argue that
in some cases, part of this behavior is due to fact the multiple core
operating system is not service oriented but a system oriented. There
is no easy way to assign a processor to do a distinct service,
undisturbed, accurate, and fast as long as the processor is an active
part of an operating system and still be a part of most of the
operating system address space.

The purpose of the OFFSCHED is to create a platform for services. For
example, assume a system is being attacked; the Linux operating system
will generate endless number of interrupts and/or softirqs to analyze
the traffic and throw out bad packets. This is on the expense of good
packets. Have you ever tried to ssh an attacked machine? Who protects
the operating system? What if we can simply do the packet analysis
outside the operating system without being interrupted? Why not assign
a core to do only fire-walling? Or just routing? Design a new type of
Real Time system? Maybe assign it as an ultra accurate timer? Create a
delaying service that does not just spin? Offload a TCP stack? Perhaps
a new type of a locking scheme? New type bottom-halves? Debug a
running kernel through an offloaded processor? Maybe assign a GPU to
do other things than just graphics? Amdahl Law teaches us that linear
speed-up is not very feasible, so why not spare a processor to do
certain tasks better? Technologically speaking, I am referring to the
Linux kernel ability to virtually hot unplug a (SMT) processor; but
instead of letting it wonder in endless "halts", assign it a service.
Server virtualization has been widely adopted by the market, and the
number of servers running virtual machines is increasing daily. As
machine virtualization gains popularity, the hypervisor itself, along
with its management stack, becomes a basic and required part of the
system. The next natural evolution phase in the virtualization
abstraction chain is to view the hypervisor as part of the user
workload, and to be able to run multiple hypervisors inside virtual
machines, each with its own set of nested guest virtual machines.

We meet in Taub (CS Faculty) building, room 6. For instructions see:

Attendance is free, and you are all invited!


Future  Haifux events include:

18/01/10 The FOSS Community as a Social Phenomenon: Yaron Dishon
15/02/10 VoIP in Linux: Rami Rosen


We are always interested in hearing your talks and ideas. If you wish to
give a talk, hold a discussion, or just plan some event haifux might be
interested in, please contact us at webmaster at haifux.org

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