bge(4) sysctl tuneables -- a blast from the past.

[Sepherosa Ziehau]

On Tue, Apr 16, 2013 at 1:56 PM, Bruce Evans <brde at optusnet.com.au> wrote:
>
> Technical bugs include:
> - wrong defaults are claimed for *coal_ticks.  The defaults are 150, but
>   are claimed to be 150 milliseconds.  These values are dimensionless,
>   but since ticks take 1 microsecond each, 150 gives 150 microseconds,
>   not 150 milliseconds.

The real effect of TX coalesce ticks is confusing to me; TX interrupt
does not come at the rate you have specified, at least for several
PCI-e bge(4) I have tested. However, RX coalesce ticks work as
expected.

Here is how the tests were conducted:
- Send only test, no RX
- Each packet consume only one BD; UDP datagram, using hardware
checksum offloading
- TX coalesce BDs is set to 0, so only TX coalesce ticks have effect

The interrupt rate I had got seemed to be related to packet size?!  I
had tested two TX coalesce ticks settings:
(the result I had recorded was using BCM5720)

The first setting was 1023us; the first col is UDP data size, the
second col is rough interrupt rate
18B    667/s
64B    611/s
128B    538/s
256B    432/s
512B    311/s
1024B    194/s
1472B    146/s

Tecond setting was 128us; the first col is UDP data size, the second
col is rough interrupt rate
18B    1647/s
64B    1338/s
128B    1030/s
256B    700/s
512B    430/s
1024B    235/s
1472B    169/s

Well, to be frank, it does not make too much sense to me.

I also twisted the HCC_MODE CLRTICK_TX a bit, but didn't get determined result.

(davidch is CC'd)

Best Regards,
sephe

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