[microblaze-uclinux] FSL Driver Overhead

[Jonathan Jung <jwjung@xxxxxxxxxxxxx>]

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Hi List,

I've had good success implementing a hardware accelerated version of  
Openssl on my Virtex II Pro FPGA via uClinux.  However, I'm  
wondering  if anybody has experience with the amount of overhead  
involved FSL reading/writing.

For example, encrypting a 700KB file in software takes (using AES):

real 2m 9.96s
user 1m 33.98s
sys 0m 33.29s (file read/writes)

Encrypting the same 700 KB file with software/hardware takes:

real 3m 23.51s
user 0m 10.40s
sys 1m 56.57s (file read/writes, FSL read/write)

As you can see, software version consumes 1m 33 s of CPU time running  
the openssl code.  The hardware/software combo takes only 10 seconds  
of time executing the openssl code, but requires 1 minute and 56  
seconds of overhead in unrelated system calls, I'm sure is because of  
the reading and writing to the FSL.

Each 64 bits of data encrypted requires 4 FSL writes, and 8 FSL  
Reads.  The initial one time setup requires 60 FSL writes.

The hardware is quite fast, running at 100 Mhz, and requires only  
about 30 cycles to process the data.

The profiler in uClib isn't active anymore, so I can't use that to do  
a line by line check for the time it takes for each write, but a best  
estimate is it takes almost a minute and half to do all those reads  
and writes.  Am I doing something funny, or is that just the amount  
of overhead required?  I'm only doing the initial drive init once  
throughout the whole process.  The FSL driver doesn't look like it's  
doing too many crazy things to write to the FSL, so I wouldn't think  
that would be the time consumer.

Any FSL related performance comments are welcome!

Thanks again to John for the excellent driver.

Jonathan


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