[HAIFUX LECTURE] OFFSCHED - Offline Scheduler by Raz Ben-Yehuda
Eli Billauer
eli at billauer.co.il
Sun Jan 3 12:47:59 IST 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
Abstract
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:
http://www.haifux.org/where.html
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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