Re: GigE Performance Comparison of GMAC and SUNGEM Drivers

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

>
>
>Hi,
>
>> The GMAC driver had significantly better performance.  It sustained
>> 663 Mbps for the 60 second test period, and used 63 % of the CPU on
>> the transmitter and 64 % of the CPU on the receiver.  By comparison,
>> the SUNGEM driver only achieved 588 Mbps, and utilized 100 % of the
>> CPU on the transmitter and 86 % of the CPU on the receiver.  Thus,
>> the SUNGEM driver had an 11.3 % lower network performance while
>> using 58.7 % more CPU (and was in fact totally CPU saturated).

This is weird and unexpected as GMAC will request interrupt for each
transmitted packet while sungem won't

However, I noticed that sungem is getting a lot of rxmac and txmac
interrupts, I'll investigate this a bit more.

(Could you check the difference of /proc/interrupts between a test
with gmac and a test with sungem ?)

Note that I just updated sungem in my rsync tree, it now has all of
the power management and ethtool/miitool support.
I plan to replace gmac with sungem completely, so it would be nice to
figure out where that problem comes from.

Ben.


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