Robert Watson wrote:
On Sat, 9 Oct 2010, David Xu wrote:
Create a global thread hash table to speed up thread lookup, use
rwlock to protect the table. In old code, thread lookup is done with
process lock held, to find a thread, kernel has to iterate through
process and thread list, this is quite inefficient.
With this change, test shows in extreme case performance is
dramatically improved.
Could you say a little more about which workloads this helps with?
Obviously, things that look up thread IDs, but since I'm less familiar
with the threading code, a hand-wave would give me useful intuitions!
BTW, my experience with switching to read-write locking in the pcbinfo
hash lookup is that it made a huge difference, and that I experience
only fairly incremental performance changes on <= 8 cores by trying to
go to more refined models (such as encouraging CPU affinity for table
entries, etc).
Robert
I have tested it with my simple benchmark program:
http://people.freebsd.org/~davidxu/tidhash/sigperf.c
run it with following command:
/usr/bin/time ./sigperf 150 20000
result before the change:
http://people.freebsd.org/~davidxu/tidhash/thread_find.txt
after the change:
http://people.freebsd.org/~davidxu/tidhash/tfind.txt
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