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SubjectRe: multi-queue scheduler update
As promised, here are some numbers for low thread counts from the
benchmark Andrew and Davide provided. I ran the benchmark for
1,2,4 and 8 threads. I ran the test 5 times for each thread count
and used 60 seconds as the measure time in each case.

2.4.0
-----
1 1785408 1785408 0 0.000000
1 1786130 1786130 0 0.000000
1 1786156 1786156 0 0.000000
1 1781575 1781575 0 0.000000
1 1780079 1780079 0 0.000000
2 1873405 936702 0 0.000000
2 2006473 1003236 0 0.000001
2 1953842 976921 0 0.000004
2 1951338 975669 0 0.000000
2 1887887 943943 0 0.000004
4 1936350 484087 0 0.000055
4 1814430 453607 0 0.000087
4 1972681 493170 0 0.000055
4 1951748 487937 0 0.000206
4 1862182 465545 0 0.000283
8 2917216 364652 0 0.000008
8 2655834 331979 0 0.000018
8 3026734 378341 0 0.000005
8 3010204 376275 0 0.000004
8 2569647 321205 0 0.000014
2.4.0-multi-queue
-----------------
1 1295498 1295498 0 0.000000
1 1295011 1295011 0 0.000000
1 1296768 1296768 0 0.000000
1 1296053 1296053 0 0.000000
1 1296472 1296472 0 0.000000
2 1999043 999521 0 0.000000
2 1410636 705318 0 0.000000
2 1414476 707238 0 0.000000
2 2014664 1007332 0 0.000001
2 1414509 707254 0 0.000000
4 2046182 511545 0 0.000232
4 2101535 525383 0 0.000115
4 2094828 523707 0 0.000155
4 2097406 524351 0 0.000144
4 2057331 514332 0 0.000132
8 3795829 474478 0 0.000185
8 4058329 507291 0 0.001871
8 3845934 480741 0 0.000248
8 3715243 464405 0 0.000084
8 3777303 472162 0 0.000194
As expected the single thread numbers for the multi-queue scheduler
are not as good as those of the existing scheduler. However, at 2
threads it is getting pretty close and from 4 threads up, the
multi-queue scheduler does better.

In this multi-queue implementation, the amount of overhead is
related to the number of processors in the system. Therefore,
I would expect the numbers to 'be better' for low thread counts
on systems with lower (<8) processor counts. It would be
interesting to see if the point at which the multi-queue does
better stays at aprox CPUs/2 as we change system configurations.
Hopefully we will have some more extensive benchmark results in
the not too distant future. Until then, we'll be looking into
optimizations to help out the multi-queue scheduler at low
thread counts.

--
Mike Kravetz mkravetz@sequent.com
IBM Linux Technology Center
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