[Cbe-oss-dev] Required cycles for an SPE context-switch

[Michael Ellerman]

On Fri, 2008-01-18 at 17:08 +0100, csc81 at csc81.de wrote:
> Hello all :)
> 
> For my diploma thesis I would like to know the average costs of an SPE 
> context-switch on a PS3 running Fedorra Core 7 Linux (expressed in core 
> clock frequency cylces or microseconds) in absence of contention and 
> under load. A rough estimation would be sufficient. The costs should 
> include the communication over the EIB and the computational costs of 
> the linux kernel (SPE scheduler and maybe others).
> 
> My goal is to create a diagram that shows the percentage which is needed 
> for context switching on N SPEs depending on different SPE Scheduler 
> frequencies relative to the available resources on one Cell processor.
> 
> I need this information to estimate the overhead of the preemptive 
> programming model. In particular the worst case is interesting.
> 
> Does anyone know a rough value or at least a paper or a documentation 
> where I can find this information?

Section 12 of the CBE programming handbook describes the sequence:
http://www-01.ibm.com/chips/techlib/techlib.nsf/techdocs/9F820A5FFA3ECE8C8725716A0062585F

I don't know of any estimate of the cost, other than "lots". If you can
come up with a figure I think we'd all be very interested.

The best approach I think would be to instrument the kernel and/or your
spe app to measure the overhead.

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: This is a digitally signed message part
URL: <http://lists.ozlabs.org/pipermail/cbe-oss-dev/attachments/20080119/e37a84e3/attachment.pgp>