>> > Ie. the headers that don't need to go across the bus are the critical
>> > resource saved by TSO.
>>
>> I'm not sure that's entirely true in this case - the Netfinity
>> 8500R is slightly unusual in that it has 3 or 4 PCI buses, and
>> there's 4 - 8 gigabit ethernet cards in this beast spread around
>> different buses (Troy - are we still just using 4? ... and what's
>> the raw bandwidth of data we're pushing? ... it's not huge).
>>
>> I think we're CPU limited (there's no idle time on this machine),
>> which is odd for an 8 CPU 900MHz P3 Xeon,
>
> Quite possibly. The P3 has roughly an 800MB/s FSB bandwidth, that must
> be used for both I/O and memory accesses. So just driving a gige card at
> wire speed takes a considerable portion of the cpus capacity.
>
> On analyzing this kind of thing I usually find it quite helpful to
> compute what the hardware can theoretically to get a feel where the
> bottlenecks should be.
We can push about 420MB/s of IO out of this thing (out of that
theoretical 800Mb/s). Specweb is only pushing about 120MB/s of
total data through it, so it's not bus limited in this case.
Of course, I should have given you that data to start with,
but ... ;-)
M.
PS. This thing actually has 3 system buses, 1 for each of the two
sets of 4 CPUs, and 1 for all the PCI buses, and the three buses
are joined by an interconnect in the middle. But all the IO goes
through 1 of those buses, so for the purposes of this discussion,
it makes no difference whatsoever ;-)
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