aes performance

[Scott Bennett]

     On Wed, 25 Feb 2009 22:59:14 +0100 Olaf Selke <olaf.selke at blutmagie.de>
wrote:
>I wrote:
>> 
>> as I understood tor spends most of its cpu time within openssl library aes crypto.
>> Which result of "openssl speed aes" applies to tor? Is it aes-128 cbc 16 bytes?
>> In this case my old Prestonia P4 Netburst Xeon box's throughput is supposed to
>> be roughly about 40 MBit/s as middleman. Correct?
>> 
>> type             16 bytes     64 bytes    256 bytes   1024 bytes   8192 bytes
>> aes-128 cbc      84098.99k   119729.69k   138053.97k   142741.16k   144386.04k
>> aes-192 cbc      75035.35k   104143.72k   115681.81k   120099.84k   120949.42k
>> aes-256 cbc      69559.47k    92221.78k   102006.05k   105361.75k   100274.74k
>
>stupid! I mixed up openssl's benchmark bytes/s from the table above with
>bits/s network throughput. Now it appears only 10% tor's cpu usage is
>spent within aes crypto. What the heck is tor doing the remaining 90%?
>
     Olaf, your system is one of 14 or 15 tor relays that routinely peak at
more than 5 MB/s.  You have, in the past, stated that it typically has ~5,000
established connections simultaneously.  I would guess that key exchange
operations on a system loaded like that must take up an awful lot of CPU time.
     My relay peaks at about 1/10 of blutmagie's peaks.  tor's primary CPU
percentage range seems to be 0% - 13% (2-second averages) on my 3.4 GHz P4
Prescott (which is also a Netburst chip).  Occasionally, it will consume more
than that for a brief time, sometimes as much as 30% - 40%, but those events
usually last only a couple of seconds.  Given these numbers, your figures seem
reasonable.


                                  Scott Bennett, Comm. ASMELG, CFIAG
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