packet drop with intel gigabit / marwell gigabit
Jin Guojun (VFFS)
g_jin at lbl.gov
Sun Mar 19 10:45:41 UTC 2006
> CPU utilization is 0% if apache is not running and 10-20%, when
> running and
> serving 30-40 concurrent downloads (traffic is 3-4MB/s on fxp0 interface)
Is the number 3-4MB/s for per stream or the total for all 30-40 streams?
Are these downloads sent to a disk?
> i measured the network performance with 'iperf' util, started the
> server on my box
> and benchmarked with a client on the other gigabit machine.
> it showed 0% packet drop, when apache was not running and 4-7%, when
> then i checked how it behave when i shut down apache and init a local
> file copy from one
> (not system!) disk to other (not system disk either). packet drop was
> 5-10%, due to the higher load.
> so i think interrupts or just the load takes the network performance,
> but i have no clue how to fix it.
> is it possible that the 2000+ xp amd is just weak to serve such a
> traffic? (em0 traffic's maximum is 18-23MB/s)
> i think it might be around 30MB/s without packet drop.
First let's clear the notation -- Is 30MB/s (MBytes/s) = 240Mb/s
(Mbit/s) or MB/s means Mbits/s
If MB/s is MBytes/s and you also write this amount data to a disk, plus
other traffic on fxp0 to disk too,
then your problem may be bonded by memory bandwidth because CPU
utilization is low:
(240 + 24~32) x 2 is about 535 Mbit/s (some chipset/motherboard has
low memory BW for AMD)
If this is true, then this no thing you can tune. What does the chipset
(Motherboard) this machine have?
> I did FTP measurement, because what i want is to copy files with high
> speed from the
> other gigabit machine. However FTP needs resources (CPU, I/O, etc),
> but iperf not!
> iperf shows 20% CPU utilization when apache not running and when
> there's no packet drop.
> ps: Now apache says: 14 requests currently being processed
> traffic is 1MB/s on fxp0, and em0 benchmark with iperf says (64k udp
> window size):
> [ 3] 0.0-10.0 sec 235 MBytes 197 Mbits/sec
> [ 3] Sent 167375 datagrams
> [ 3] Server Report:
> [ 3] 0.0-10.0 sec 229 MBytes 192 Mbits/sec 0.066 ms
> 4115/167375 (2.5%)
> the other gigabit machine is OK, because i have 0% packet drop, when
> my machine is totally idle.
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