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SubjectRe: sched: Avoid SMT siblings in select_idle_sibling() if possible
* Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com> [2012-02-23 16:19:59]:

> > Enabling SD_BALANCE_WAKE used to be decidedly too expensive to consider.
> > Maybe that has changed, but I doubt it. (general aside: testing with a
> > bloated distro config is a big mistake)
>
> I am seeing 2.6% _improvement_ in volanomark score by enabling SD_BALANCE_WAKE
> at SMT/MC domains.

Ditto with pipe benchmark.

> Machine : 2 Quad-core Intel X5570 CPU (H/T enabled)
> Kernel : tip (HEAD at 6241cc8)

"perf bench sched pipe" was run 10 times and average ops/sec score
alongwith std. dev is noted as below.


SD_BALANCE_WAKE SD_BALANCE_WAKE
disabled enabled

Avg. score 108984.900 111844.300 (+2.6%)
std dev 20383.457 21668.604

Note:

SD_BALANCE_WAKE for SMT/MC domain was enabled by writing into appropriate
flags file present in /proc:

# cd /proc/sys/kernel/sched_domain/
# for i in `find . -name flags | grep domain1`; do echo 4671 > $i; done
# for i in `find . -name flags | grep domain0`; do echo 703 > $i; done

- vatsa



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