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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