On 04/06/12 17:13, Attilio Rao wrote:
Il 05 aprile 2012 19:12, Arnaud Lacombe<lacom...@gmail.com> ha scritto:
Hi,
[Sorry for the delay, I got a bit sidetrack'ed...]
2012/2/17 Alexander Motin<m...@freebsd.org>:
On 17.02.2012 18:53, Arnaud Lacombe wrote:
On Fri, Feb 17, 2012 at 11:29 AM, Alexander Motin<m...@freebsd.org> wrote:
On 02/15/12 21:54, Jeff Roberson wrote:
On Wed, 15 Feb 2012, Alexander Motin wrote:
I've decided to stop those cache black magic practices and focus on
things that really exist in this world -- SMT and CPU load. I've
dropped most of cache related things from the patch and made the rest
of things more strict and predictable:
http://people.freebsd.org/~mav/sched.htt34.patch
This looks great. I think there is value in considering the other
approach further but I would like to do this part first. It would be
nice to also add priority as a greater influence in the load balancing
as well.
I haven't got good idea yet about balancing priorities, but I've
rewritten
balancer itself. As soon as sched_lowest() / sched_highest() are more
intelligent now, they allowed to remove topology traversing from the
balancer itself. That should fix double-swapping problem, allow to keep
some
affinity while moving threads and make balancing more fair. I did number
of
tests running 4, 8, 9 and 16 CPU-bound threads on 8 CPUs. With 4, 8 and
16
threads everything is stationary as it should. With 9 threads I see
regular
and random load move between all 8 CPUs. Measurements on 5 minutes run
show
deviation of only about 5 seconds. It is the same deviation as I see
caused
by only scheduling of 16 threads on 8 cores without any balancing needed
at
all. So I believe this code works as it should.
Here is the patch: http://people.freebsd.org/~mav/sched.htt40.patch
I plan this to be a final patch of this series (more to come :)) and if
there will be no problems or objections, I am going to commit it (except
some debugging KTRs) in about ten days. So now it's a good time for
reviews
and testing. :)
is there a place where all the patches are available ?
All my scheduler patches are cumulative, so all you need is only the last
mentioned here sched.htt40.patch.
You may want to have a look to the result I collected in the
`runs/freebsd-experiments' branch of:
https://github.com/lacombar/hackbench/
and compare them with vanilla FreeBSD 9.0 and -CURRENT results
available in `runs/freebsd'. On the dual package platform, your patch
is not a definite win.
But in some cases, especially for multi-socket systems, to let it show its
best, you may want to apply additional patch from avg@ to better detect CPU
topology:
https://gitorious.org/~avg/freebsd/avgbsd/commit/6bca4a2e4854ea3fc275946a023db65c483cb9dd
test I conducted specifically for this patch did not showed much improvement...
Can you please clarify on this point?
The test you did included cases where the topology was detected badly
against cases where the topology was detected correctly as a patched
kernel (and you still didn't see a performance improvement), in terms
of cache line sharing?
At this moment SCHED_ULE does almost nothing in terms of cache line
sharing affinity (though it probably worth some further experiments).
What this patch may improve is opposite case -- reduce cache sharing
pressure for cache-hungry applications. For example, proper cache
topology detection (such as lack of global L3 cache, but shared L2 per
pairs of cores on Core2Quad class CPUs) increases pbzip2 performance
when number of threads is less then number of CPUs (i.e. when there is
place for optimization).
--
Alexander Motin
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