Re: DBT3-pgsql large performance improvement 2.6.6-rc1

[Andrew Morton <akpm@osdl.org>]

Mary Edie Meredith <maryedie@osdl.org> wrote:
>
> Performance in DBT-3 (using PostgreSQL) has vastly
> improved for _both in the "power" portion (single 
> process/query) and in the "throughput" portion of 
> the test (when the test is running multiple processes) 
> on our 4-way(4GB) and 8-way(8GB) STP systems as 
> compared 2.6.5  kernel results.
> 
> Using the default DBT-3 options (ie using LVM, ext2, 
> PostgreSQL version 7.4.1) 
> 
> Note: Bigger numbers are better.
> 
> Kernel....Runid..CPUs.Power..%incP.Thruput %incT 
> 2.6.5     291308   4  97.08  base   120.46  base   
> 2.6.6-rc1 291876   4  146.11 50.5%  222.94 85.1%
> 
> Kernel....Runid..CPUs.Power..%incP..Thruput %incT
> 2.6.5     291346   8  101.08  base   138.95 base
> 2.6.6-rc1 291915   8  151.69  50.1%  273.69 97.0%
> 
> So the improvement is between 50% and 97%!

How odd.

> Profile 2.6.5 8way throughput phase:
> http://khack.osdl.org/stp/291346/profile/after_throughput_test_1-tick.sort
> Profile 2.6.6-r1 8way throughput phase:
> http://khack.osdl.org/stp/291915/profile/after_throughput_test_1-tick.sort

Odder.  do_anonymous_page() is doing 10x more work in 2.6.6-rc1.  And the
CPU scheduler cost has fallen a lot.

Frankly, I can't think of anything in 2.6.6-rc1 which would cause either of
these things!

> What I notice is that radix_tree_lookup is in 
> the top 20 in the 2.6.5 profile, but not in 
> 2.6.6-rc1.  Could theradix tree changes be 
> responsible for this?

I would certainly expect 2x or even higher throughput increases from either
the writeback changes or the ext2&ext3 fsync changes.

> DBT-3 is a read mostly DSS workload and the throughput 
> phase  is where we run multiple query streams (as 
> many as we have CPUs).  In this workload, the database 
> is stored on a file system, but it is small relative 
> to the amount of memory (4GB and 8GB).  It almost 
> completely caches in page cache early on.   So there 
> is some physical IO in the first few minutes, but very 
> little to none in the remainder. 

But you're not doing a significant amount of writing during the test, so
scrub that theory.

Do you have full reports anywhere?  I'd be interested in seeing a vmstat
trace from the entire run, both 2.6.5 and 2.6.6-rc1.