Re: [microblaze-uclinux] OT?, Performance

[Matthew Rubenstein <email@xxxxxxxxxxxx>]

> However, as Matthew R. has noted, doing this in the FPGA domain gives us 
> much greater flexibility in terms of hardware acceleration.  So, a major 
> point of doing this microblaze uClinux thing is the design and 
> implementation flexibility to help us get the best of both worlds.. or 
> at least the flexibility to find a feasible mixed SW/HW solution where 
> purely SW or purely HW might be impossible (simply not enough processor 
> cycles), or impractical (build a webserver purely from logic?  Why?!)

	Beyond performance improvements, webservers might benefit from
implementation in a more testably deterministic platform, to improve
stability, reliability, and scalability, all under the rubric of greater
predictability. That said, application functions usually require more
flexibility over revision iterations than available to hardware
development, even on FPGA. So OS features are probably higher priority
targets for SW->HW migration than application features: Verilog TCP/IP
stack first, HTTP server later. However, a small-footprint httpd core
might be a better alternative than porting an httpd codebase, if the
core is already available. I personally would like to see a microkernel
OS include pluggable protocol modules for HTTP, FTP, SMTP, SSH, and
others, rather than each app reimplementing them, much as there are
pluggable windowing toolkits for client OS'es, so apps don't reinvent
the wheel each time. But for this list community, getting lower-layer
protocols, like TCP/IP, USB, VGA etc, is more urgent, important and
widely valuable than the higher level protocols that require them.


> On Wed, 2004-05-12 at 18:13, John Williams wrote:
> Hi Emanuel,
> 
> emanuel stiebler wrote:
> 
> >> On Wed, 12 May 2004, emanuel stiebler wrote:
> >>
> >>> Anybody had some thoughts already, why there is such a BIG
> >>> difference between the numbers on xilinx web, and the dhrystones
> >>> we measure here ?
> 
> > Between the "grades" there is a difference of few percent.
> > I'm talking about a difference bewteen 600 KMIPS and 50 KMIPS ...
> 
> I'm speculating, but the benchmarks posted on the xilinx website will be 
> for bare metal implementations, just the benchmark code running directly 
> on the microblaze (no OS), probably from BRAM memory space, and probably 
> utilising the microblaze's native harvard-style split instruction/data 
> bus topology.  It is likely that the interrupt pin is not even 
> connected...
> 
> On the other hand, the dhrystone application running under uclinux is 
> being scheduled alongside any other processes, there are at least 4 
> devices capable of interrupting the processor (including the timer which 
> does so every 10ms), there is interrupt dispatch code that must run 
> every time, we tie the instruction and data buses together (von-neumann 
> architecture), run from external DDR using BRAM only as cache, and so on.
> 
> Basically, it's the computational efficiency penalty of using a full 
> operating system.  As embedded systems designers, it's our job to assess 
> the performance tradeoff against whatever it is we gain from using 
> something like uClinux (interoperability, standard development platform, 
> application portability etc etc).
> 
> However, as Matthew R. has noted, doing this in the FPGA domain gives us 
> much greater flexibility in terms of hardware acceleration.  So, a major 
> point of doing this microblaze uClinux thing is the design and 
> implementation flexibility to help us get the best of both worlds.. or 
> at least the flexibility to find a feasible mixed SW/HW solution where 
> purely SW or purely HW might be impossible (simply not enough processor 
> cycles), or impractical (build a webserver purely from logic?  Why?!)
> 
> That said, there's still plenty of room for optimisation in the 
> microblaze-specific parts of the kernel port.
> 
> Regards,
> 
> John
> 
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-- 


(C) Matthew Rubenstein

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