Re: packet drop with intel gigabit / marwell gigabit


Arne Woerner wrote:

--- "Jin Guojun [VFFS]" [1]<g_jin@xxxxxxx> wrote:
In you example:


Now your 1.6 GB/s reduced to 16MB/s or even worse just based
on this factor.



What did we show by this <<dd if=/dev/zero ...>> test? I thought
that would prove the memory bandwidth is about 8Gbit/sec
(1GByte/sec; 2 * <dd's bytes/sec number>/2^30).


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=4m count=100
tests memory bandwidth if your cache is less than 2 MB
Now you may give me the real memory bandwidth on your system :-)
I would expect something around 500.
Notice that your memory copy speed will be one half of it.
/dev/null device really does nothing beside throwing away data.
That is, it can be counted as a cost for system call.
-Jin

References

1. mailto:g_jin@xxxxxxx
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