Re: [microblaze-uclinux] Performance microblaze vs. VirtexIIPro

[John Williams <jwilliams@xxxxxxxxxxxxxx>]

Hi Josef, emanuel,

jozsef imrek wrote:

> On Tue, 11 May 2004, emanuel stiebler wrote:
> 
>>Anaybody out here made some tests what the performance in
>>dhrystones is of this "chips" ?

> there is a config option in the uClinux-dist that you can use to have a
> dhrystones test. i switchd it on, run the test (the header says: Dhrystone
> Benchmark, Version 2.1 (Language: C) ).
> 
> the fpga is a xc2v1000fg456-4 runing at 66Mhz.
> 
> at boot time the kernel measures 3.19 BogoMIPS.

You can multiply this bogoMIPs by a factor of 10 if you enable the 
instruction cache.  dcache has a very small effect, maybe <1 bogoMIPs.

> the result is 5035.0 dhrystones/sec (see attached output from the test).

Similarly the dhrystone measures are greatly improved if you enable the 
icache - without it, and running from external DDR, poor little 
microblaze lives in a perpetual pipeline stall.

A note on the dhrystones, and an item for the wishlist - there is a 
problem with time accounting in the kernel - if you run dhrystone under 
zero load, the system clock time reported for execution of the benchmark 
is pretty accurate (compared to wall clock time).

If you place the kernel under a ping flood attack the reported system 
time is unchanged, but the actual wall clock time doubles!

I've never looked further into it, but it certainly should be 
straightened out, especially if you are relying on the system timer to 
even vaguely represent true time.  This may be a common problem, which 
could explain why people put RTC chips in their systems if it really 
matters.  Comments?

Regards,

John
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