Re: Database regression due to scheduler changes ?

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David Lang wrote:
On Tue, 8 Nov 2005, Nick Piggin wrote:


Long lived and memory intensive cloned or forked tasks will often
[but far from always :(] want to be put on another memory controller
from their siblings.

On workloads where there are lots of short lived ones (some bloated
java programs), the load balancer should normally detect this and
cut the balance-on-fork/clone.


although if the primary workload is short-lived tasks and you don't do balance-on-fork/clone won't you have trouble ever balancing things? (anything that you do move over will probably exit quickly and put you right back where you started)


You'll have no trouble if things *need* to be balanced, because
that would imply the runqueue length average is significantly
above the lengths of other runqueues.

As far as the extra test goes, it's really a miniscule overhead
compared with the fork / clone cost itself, and can be really
worthwhile if we get it right.


Of course there are going to be cases where this fails. I haven't
seen significant slowdowns in tests, although I'm sure there would
be some at least small regressions. Have you seen any? Do you have
any tests in mind that might show a problem?


even though people will point out that it's a brin-dead workload (that should be converted to a state machine) I would expect that most fork-per-connection servers would show problems if the work per connection is small


Well it may be brain-dead, but if people use them (and they do)
then I would really be interested to see results.

I did testing with some things like apache and volanomark, however
I was not able to make out much difference on my setups. Though
obviously that's not to say that there won't be with other software
or other workloads / architectures etc.

--
SUSE Labs, Novell Inc.

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