Date:	Wed, 26 Aug 2009 17:54:03 +0300
From:	raz ben yehuda <raziebe@...il.com>
To:	Maxim Levitsky <maximlevitsky@...il.com>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Chris Friesen <cfriesen@...tel.com>,
	Mike Galbraith <efault@....de>, riel@...hat.com, mingo@...e.hu,
	andrew motron <akpm@...ux-foundation.org>,
	wiseman@...s.biu.ac.il, lkml <linux-kernel@...r.kernel.org>,
	linux-rt-users@...r.kernel.org
Subject: Re: RFC: THE OFFLINE SCHEDULER


On Wed, 2009-08-26 at 17:45 +0300, Maxim Levitsky wrote:
> On Wed, 2009-08-26 at 09:47 -0400, Christoph Lameter wrote:
> > On Wed, 26 Aug 2009, raz ben yehuda wrote:
> > 
> > > How will the kernel is going to handle 32 processors machines ?  These
> > > numbers are no longer a science-fiction.
> > 
> > The kernel is already running on 4096 processor machines. Dont worry about
> > that.
> > 
> > > What i am suggesting is merely a different approach of how to handle
> > > multiple core systems. instead of thinking in processes, threads and so
> > > on i am thinking in services. Why not take  a processor and define this
> > > processor to do just firewalling ? encryption ? routing ? transmission ?
> > > video processing... and so on...
> > 
> > I think that is a valuable avenue to explore. What we do so far is
> > treating each processor equally. Dedicating a processor has benefits in
> > terms of cache hotness and limits OS noise.
> > 
> > Most of the large processor configurations already partition the system
> > using cpusets in order to limit the disturbance by OS processing. A set of
> > cpus is used for OS activities and system daemons are put into that set.
> > But what can be done is limited because the OS threads as well as
> > interrupt and timer processing etc cannot currently be moved. The ideas
> > that you are proposing are particularly usedful for applications that
> > require low latencies and cannot tolerate OS noise easily (Infiniband MPI
> > base jobs f.e.)
> 
> My 0.2 cents:
> 
> I have always been fascinated by the idea of controlling another cpu
> from the main CPU.
> 
> Usually these cpus are custom, run proprietary software, and have no
> datasheet on their I/O interfaces.
> 
> But, being able to turn an ordinary CPU into something like that seems
> to be very nice.
> 
> For example, It might help with profiling. Think about a program that
> can run uninterrupted how much it wants.
> 
> I might even be better, if the dedicated CPU would use a predefined
> reserved memory range (I wish there was a way to actually lock it to
> that range)
> 
> On the other hand, I could see this as a jump platform for more
> proprietary code, something like that: we use linux in out server
> platform, but out "insert buzzword here" network stack pro+ can handle
> 100% more load that linux does, and it runs on a dedicated core....
> 
> In the other words, we might see 'firmwares' that take an entire cpu for
> their usage.
This is exactly what offsched (sos) is. you got it. SOS was partly inspired by the notion of a GPU. 
Processors are to become more and more redundant and Linux as an
evolutionary system must use it. why not offload raid5 write engine ?
why not encrypt in a different processor ?
Also , having so many processors in a single OS means a bug prone
system , with endless contention points when two or more OS processors
interacts. let's make things simpler.
> > 
> > 
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