Re: peculiar server "bandwidth" posted by server "mnl" and possible new type of attack

[Olaf Selke <olaf.selke@xxxxxxxxxxxx>]

Scott Bennett wrote:
> 
>      Nearly 49 MB/s seems a bit of a stretch.  The server's operator sent me
> a note saying that the server is attached to the 1 GB/s campus backbone net,
> but it is attached via a 100 Mb/s router, so the reported data rate is four
> to five times the rate physically possible due to the router's limitation.
> The server, according to its operator, is running on a 2.6 GHz P4, and its
> descriptor says the machine is running LINUX.  Based upon postings quite a
> while back from blutmagie's operator and from a few other operators of very
> high-data-rate servers, it seems to me that a 2.6 GHz P4 (Northwood?) running
> LINUX would not be capable of handling a load eight to ten times that of
> blutmagie, regardless of its network connection's capacity.

blutmagie tor node is running on a pair of the old Prestonia P4 NetBurst Xeon DP
3200MHz processors. Over the last four weeks mrtg monitoring is showing an
average interface throughput of 32 MBit/s in and 33 MBit/s out. Throughput is
limited by cpu power rather than by available network bandwidth. Since Tor
doesn't scale very well with the number of cores, one core is loaded with 100%,
leaving the other three cores almost idle. Compiling the openssl library with
Intel's C compiler icc improved performance by about 20-25% compared with gcc
(compiling tor with icc doesn't change very much). That's the reason blutmagie's
observed data rate increased from about 5500 to nearly 7000 KByte/s some weeks ago.

regards Olaf