linux thread scheduling

[Xin Tong]

I have a program that spawns 3 threads and there is a great deal of
sharing among the three threads. they all read/update a couple of
shared variables.

I run this on nehalem (8 cores, 4 core in each physical package),  I
find that running the 3 threads on core 0, 1, 2 (using
pthread_setaffinitiy) gives much better results, this is because the
cache coherency protocol performs much better on the same package.
However, if  I leave Linux (Suse Enterprise) to schedule it. it gives
much worse performance, i suspect that linux is scheduling the 3
threads across the physical packages ( 2 on one package, 1 on
another). Is this possible ? why does linux do this ?

Thanks

Xin
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/