Possible Threading problem with -CURRENT / MySQL?

[JG]

I just posted this to -AMD64 and someone brought this discussion to my 
attention...
anyway I'll repost it here since it seems to be a more relevant discussion:


I got a couple emails from people telling me I should retest
because some changes have been committed recently that
might effect my MySQL benchmarks.

Well I just did a buildworld and kernel to -CURRENT & it did
effect the results alright... just not the way we wanted them to:

amd64f# super-smack update-select.smack 30 10000

Query Barrel Report for client smacker
connect: max=46ms  min=2ms avg= 26ms from 30 clients
Query_type      num_queries     max_time        min_time        q_per_s
select_index    300000  2       0       958.05
update_index    300000  2       0       958.05


In all my previous tests I think that number was at least 2000/qps
(and that was bad) and as much as 4000/qps.

Whatever was changed recently really killed performance in this area.

This is a SMP kerenel using SCHED_ULE.
.. debugging is turned off in kernel of course.


Whatever was changed is producing very erratic benchmark results
from bad to worse.... here is an example:  (keep in mind this box
is for testing only, nothing else is going on on this box)

I ran some short tests below (notice 100 below vs 10000 above)

amd64f# super-smack update-select.smack 30 100
Query Barrel Report for client smacker
connect: max=24ms  min=2ms avg= 10ms from 30 clients
Query_type      num_queries     max_time        min_time        q_per_s
select_index    3000    1119    0       60.64
update_index    3000    2185    0       60.64

amd64f# super-smack update-select.smack 30 100
Query Barrel Report for client smacker
connect: max=292ms  min=1ms avg= 54ms from 30 clients
Query_type      num_queries     max_time        min_time        q_per_s
select_index    3000    4       0       3167.06
update_index    3000    1       0       3167.06

amd64f# super-smack update-select.smack 30 100
Query Barrel Report for client smacker
connect: max=26ms  min=3ms avg= 10ms from 30 clients
Query_type      num_queries     max_time        min_time        q_per_s
select_index    3000    1891    0       32.73
update_index    3000    1891    0       32.73
amd64f#

amd64f# super-smack update-select.smack 30 100
Query Barrel Report for client smacker
connect: max=37ms  min=3ms avg= 10ms from 30 clients
Query_type      num_queries     max_time        min_time        q_per_s
select_index    3000    10      0       757.05
update_index    3000    11      0       757.05

amd64f# super-smack update-select.smack 30 100
Query Barrel Report for client smacker
connect: max=39ms  min=5ms avg= 15ms from 30 clients
Query_type      num_queries     max_time        min_time        q_per_s
select_index    3000    11      0       2988.89
update_index    3000    2       0       2988.89

Those were ran one after the other with nothing changed in between.


Just thought I would give you guys a heads up.