Re: Subject: PATCH : offline scheduler

[raz ben yehuda <raziebe@013.net>]

first , i really appreciate having Len Brown reading my paper. you also
have my sympathy :)
On Sat, 2009-04-18 at 00:44 -0400, Len Brown wrote:
> On Sat, 18 Apr 2009, raz ben yehuda wrote:
> 
> > Len Hello 
> > offsched is a platform aimed to assign a service to an off-lined processor.
> > Motivation is explained in: 
> > http://sos-linux.svn.sourceforge.net/viewvc/sos-linux/offsched/trunk/Documentation/OFFSCHED.pdf
> > Currently I have implemented two services:
> > 
> > HYBRID REAL TIME LINUX 
> > Implemented as a A 1us timer. This timer shows how a true real time system may co-exist with a 
> > regular linux server. This way there is no enforcement of a real time system requirements on the
> > entire kernel. Full documentation is at:
> > http://sos-linux.svn.sourceforge.net/viewvc/sos-linux/offsched/trunk/Documentation/OFFSCHED-RT.pdf
> > 
> > RTOP
> > This piece of software send system statistics to a remove server.
> > The user benefit is that even if the machine is un-accessible (remotely or locally) 
> > RTOP still sends system statistics to a remote server. I have showed in a small paper what RTOP is:
> > http://sos-linux.svn.sourceforge.net/viewvc/sos-linux/offsched/trunk/Documentation/OFFSCHED-RTOP.pdf
> > 
> > The patch is mostly a facility for offsched. The exporting of tasklist_lock is because RTOP is implemented as a driver
> > and it must lock the tasks list.
> > This is the 4-th post. I will be grateful for your reply.
> > 
> > Signed-off-by: Raz Ben Yehuda <raziebe@013.net.il>
> > 
> > arch/x86/kernel/process.c |   42 ++++++++++++++++++++++++++++++++++++++++++
> > arch/x86/kernel/smpboot.c |   11 +++++++----
> > include/linux/cpu.h       |   20 ++++++++++++++++++++
> > include/linux/sched.h     |    2 +-
> > kernel/cpu.c              |    1 +
> > kernel/fork.c             |    6 ++++++
> > 6 files changed, 77 insertions(+), 5 deletions(-)
> 
> 
> Interesting project Raz, must have been fun to develop!
> 
> A couple of comments...
> 
> It would probably be of most interest to Ingo and the RT guys on
> linux-rt-users@vger.kernel.org rather than the ACPI guys
> on linux-acpi@vger.kernel.org. (cc updated)
> 
> I don't understand the utility of the "offline timer"
> use in section 6.1 of the paper.
> With Nehalem, Intel is finally shipping a hardware TSC that is
> guaranteed to be C-state, P-state, T-state invarient and not to drift --
> so an extremely accurate cycle counter is just an MSR read away
> on all cores...
> 
I was not clear . I meant timer and not a clock. Having a more accurate
TSC is even better, because reading from hpet or cmos clocks
takes too long time.
> I also don't understand 6.2, the system monitor use --
> for the hardware also provides numerous perfmon counters
> in hardware for monitoring, and exposing those in a friendly way
> seems to me to be a more interesting exercise than
> trying to do monitoring in software with a dedicated CPU.
rtop is meant to be used only when you cannot access the machine because it is 
too overloaded. RTOP pushes information out from the system.
> For 6.3, the traffic shaper...
> The newer NICs have dedicated hardware to detect and shape
> traffic flows -- again, probably much more efficient than
> dedicating a general purpose processor...
You are correct.I think i will design a new kind of offlet, one than can offload 
the entire tcp stack, this way i will have nice ultra fast web server. I
cannot rely on TOE as a general solution for all interfaces. and I do
not think TOE is support ether channeling.  
> For RT...
> Certainly the performance of a dedicated CPU would be
> what the rt kernel would want to strive for.  I guess
> the question is if you can measure an actual performance
> difference to quanitfy the theoretical beneifts
> of the lack of locks, lack of protection etc.
well, you are correct , again. i will provide benchmarks(if my 
tutor will allow me to change my plans that is).
> cheers,
> Len Brown, Intel Open Source Technology Center
> 
>