packet drop with intel gigabit / marwell gigabit

[Jin Guojun [VFFS]]

   Arne Woerner wrote:

     It depends on how you use /dev/zero.

  dd of=/dev/null if=/dev/zero bs=4k count=100k
tests cache speed
    

% dd of=/dev/null if=/dev/zero bs=4k count=100k
102400+0 records in
102400+0 records out
419430400 bytes transferred in 0.204511 secs (2050894814
bytes/sec)
about 32Gbit/sec?

   If you have 1.8-19.GHz 32-bit CPU with 2 level caches,
   16 Gb/s cache speed is about right, not 32 (2x8=16).

  dd of=/dev/null if=/dev/zero bs=4m count=100
tests memory bandwidth if your cache is less than 2 MB

  
% dd of=/dev/null if=/dev/zero bs=4m count=100
100+0 records in
100+0 records out
419430400 bytes transferred in 2.587341 secs (162108677 bytes/sec)
about 2.4Gbit/sec?

I had an mpeg encoder in the background, when i did those
benchmarks... :-)

  

Now you may give me the real memory bandwidth on your
system :-)
I would expect something around 500.

    

Hmm... 500Mbit/sec? even if i divide 2.4Gbit by 4, i still get
600Mbit/sec on a quite busy (50%) system...

  

   All previous notations are MB, not Mb.
   Also, 1 Byte is 8 bits not 4 bits. :-)
   Even after your program finished, you had only 277 MB/s (DDR memory?),
   which is far below a good motherboard. Good motherboards should
   have 500 - 900 MB/s memory bandwidth, while expensive motherboards
   can have 1-3 GB/s memory bandwidth, which are suitable for 10 Gb/s
   NIC.
   It sounds like you have a A7V8X or similar motherboard, Do you?
       -Jin