Re: [tor-relays] high cpu usage, normal ?

[Scott Bennett <bennett@xxxxxxxxxx>]

     On Tue, 5 Apr 2011 14:56:42 +0200 Gijs Peskens <gpeskens85@xxxxxxxxx>
wrote:
>I'm running an exit relay configured to give up to 6,4MB/s on an Athlon64
>3000+ Freebsd box, and I'm seeing cpu usage between 30-60% is this
>considered normal ? Any means of getting it down? (except getting a faster

     For such a high-throughput node on such an old CPU, yes, that is not
only normal, but actually quite low CPU usage.

>cpu or hardware crypto)

     I don't remember whether the 3000+ is a K10-type CPU or later.  If it
is, then make sure you have superpages support enabled in your kernel at
boot time.  If the 3000+ is pre-K10, then enabling superpages support is
as likely to hurt performance as it is to help it, which basically would
leave you the option of trying it both ways to see which worked better for
you.
     On a K10 or later style of CPU, running a high-throughput node with
superpages enabled should shave 10% to 30% from whatever tor's current usage.
IOW, if you're seeing 30% - 60% now, then what you see with superpages enabled
would probably fall into the 21% - 54% range.
     The problem with AMD's pre-K10 CPUs is that the size of the TLB shrinks
when 4 MB pages are used, so that instead of having 64 entries for text pages
and 64 entries for data/stack pages, there are only two (maybe just one--I
don't recall for sure) entries for each.  Because tor is a much larger process
than would fit into one 4 MB page of each kind, using the 4 MB page size
instead of the 4 KB page size is very likely to drastically increase the
frequency of full address translations, rather than reducing it as on later
CPUs in which the TLB retains the capacity for both page sizes.
     To enable the use of superpages, your system must be at 7.2-RELEASE or
later of FreeBSD.  Just add the following to /boot/loader.conf, and then
reboot.

# enable superpages (4 MB) for large processes
vm.pmap.pg_ps_enabled=1


                                  Scott Bennett, Comm. ASMELG, CFIAG
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