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SubjectRe: Network performance degradation from 2.6.11.12 to 2.6.16.20

On Mon, 26 Jun 2006, Andi Kleen wrote:

>> I encountered the same problem on a dual core opteron equipped with a
>> broadcom NIC (tg3) under 2.4. It could receive 1 Mpps when using TSC
>> as the clock source, but the time jumped back and forth, so I changed
>> it to 'notsc', then the performance dropped dramatically to around the
>> same value as above with one CPU saturated. I suspect that the clock
>> precision is needed by the tg3 driver to correctly decide to switch to
>> polling mode, but unfortunately, the performance drop rendered the
>> solution so much unusable that I finally decided to use it only in
>> uniprocessor with TSC enabled.
>
> 2.6 is more clever at this than 2.4. In particular it does the timestamp
> for each packet only when actually needed, which is relativelt rare.
>
> Old experiences do not always apply to new kernels.

Note, that I experinced this problem on 2.6.

Actually the change happens between kernel version 2.6.15 and 2.6.16. And
is a result of Andi's changes to arch/x86_64/Kconfig and
drivers/acpi/Kconfig, which "allows/activates" the use of the timer on
x86_64.

Cheers,
Jesper Brouer

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MSc. Master of Computer Science
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