Here are the results of a 40 byte udpping (http://gentwo.org/ll) run on
kernel from 2.6.22 to 2.6.30-rc3 on a Dell 1950 dual quad core 3.3Ghz.
One system fixed 2.6.22 kernel version on the other are varied.

Nice graph at http://gentwo.org/results/udpping-results.pdf

Summary:
- Loss of ~1.5usec on fastest path (same cpu) since 2.6.22
- Different cpu same core looses 2-3 usecs vs. same cpu
- Different cpu different core looses ~ 8 usecs vs same cpu
- Maximum is usual if threads are on different sockets but sometimes
  the same socket different core is worse (2.6.26/2.6.27).
- Up to 9 usecs variance in a basic network operation just because
  of process placement.

Same CPU
Kernel		Test 1	Test 2	Test 3	Test 4	Average
2.6.22		83.03	82.9	82.89	82.92	82.94
2.6.23		83.35	82.81	82.83	82.86	82.96
2.6.24		82.66	82.56	82.64	82.73	82.65
2.6.25		84.28	84.29	84.37	84.3	84.31
2.6.26		84.72	84.38	84.41	84.68	84.55
2.6.27		84.56	84.44	84.41	84.58	84.5
2.6.28		84.7	84.43	84.47	84.48	84.52
2.6.29		84.91	84.67	84.69	84.75	84.76
2.6.30-rc2	84.94	84.72	84.69	84.93	84.82
2.6.30-rc3	84.88	84.7	84.73	84.89	84.8

Same core, different processor (l2 is shared)
Kernel		Test 1	Test 2	Test 3	Test 4	Average
2.6.22		84.6	84.71	84.52	84.53	84.59
2.6.23		84.59	84.5	84.33	84.34	84.44
2.6.24		84.28	84.3	84.38	84.28	84.31
2.6.25		86.12	85.8	86.2	86.04	86.04
2.6.26		86.61	86.46	86.49	86.7	86.57
2.6.27		87	87.01	87	86.95	86.99
2.6.28		86.53	86.44	86.26	86.24	86.37
2.6.29		85.88	85.94	86.1	85.69	85.9
2.6.30-rc2	86.03	85.93	85.99	86.06	86
2.6.30-rc3	85.73	85.88	85.67	85.94	85.81

Same Socket, different core (l2 not shared)
Kernel		Test 1	Test 2	Test 3	Test 4	Average
2.6.22		90.08	89.72	90	89.9	89.93
2.6.23		89.72	90.1	89.99	89.86	89.92
2.6.24		89.18	89.28	89.25	89.22	89.23
2.6.25		90.83	90.78	90.87	90.61	90.77
2.6.26		90.51	91.25	91.8	91.69	91.31
2.6.27		91.98	91.93	91.97	91.91	91.95
2.6.28		91.72	91.7	91.84	91.75	91.75
2.6.29		89.85	89.85	90.14	89.9	89.94
2.6.30-rc2	90.78	90.8	90.87	90.73	90.8
2.6.30-rc3	90.84	90.94	91.05	90.84	90.92

Different Socket
Kernel		Test 1	Test 2	Test 3	Test 4	Average
2.6.22		91.64	91.65	91.61	91.68	91.645
2.6.23		91.9	91.84	91.92	91.83	91.873
2.6.24		91.33	91.24	91.42	91.38	91.343
2.6.25		92.39	92.04	92.3	92.23	92.240
2.6.26		90.64	90.57	90.6	90.08	90.473
2.6.27		91.14	91.26	90.9	91.09	91.098
2.6.28		92.3	91.92	92.3	92.23	92.188
2.6.29		90.57	89.83	89.9	90.41	90.178
2.6.30-rc2	90.59	90.97	90.27	91.69	90.880
2.6.30-rc3	92.08	91.32	91.21	92.06	91.668

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html