The boot-time migration cost auto-tuning stuff seems to have
been merged to Linus' tree since 2.6.15. On little one- or
two-processor systems, the time required to measure the
migration costs isn't very noticeable, but by the time we
get to even a four-processor ia64 box, it adds about
30 seconds to the boot time, which seems like a lot.
Is that expected? Is the information we get really worth
that much? Could the measurement be done at run-time
instead? Is there a smaller hammer we could use, e.g.,
flushing just the buffer rather than the *entire* cache?
Did we just implement sched_cacheflush() incorrectly for
ia64?
Only ia64, x86, and x86_64 currently have a non-empty
sched_cacheflush(), and the x86* ones contain only "wbinvd()".
So I suspect that only ia64 sees this slowdown. But I would
guess that other arches will implement it in the future.
Bjorn
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