Date: Wed, 22 Mar 2006 10:23:21 -0800 From: "Jin Guojun [VFFS]" <g_jin@lbl.gov> To: Arne Woerner <arne_woerner@yahoo.com> Cc: freebsd-performance@freebsd.org, Gary Thorpe <gthorpe@myrealbox.com>, oxy@field.hu Subject: Re: packet drop with intel gigabit / marwell gigabit Message-ID: <44219619.7020900@lbl.gov> In-Reply-To: <20060322175336.59008.qmail@web30309.mail.mud.yahoo.com> References: <20060322175336.59008.qmail@web30309.mail.mud.yahoo.com>
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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
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