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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