High CPU usage / load average after upgrading to Ubuntu 12.04

Hello,

We upgraded from Ubuntu 11.04 to Ubuntu 12.04 and almost immediately obeserved increased CPU usage and significantly higher load average on our database server.
At the time we were on Postgres 9.0.5. We decided to upgrade to Postgres 9.2 to see if that resolves the issue, but unfortunately it did not.

Just for illustration purposes, below are a few links to cpu and load graphs pre and post upgrade.

https://s3.amazonaws.com/iqtell.ops/Load+Average+Post+Upgrade.png
https://s3.amazonaws.com/iqtell.ops/Load+Average+Pre+Upgrade.png

https://s3.amazonaws.com/iqtell.ops/Server+CPU+Post+Upgrade.png
https://s3.amazonaws.com/iqtell.ops/Server+CPU+Pre+Upgrade.png

We also tried tweaking kernel parameters as mentioned here - http://www.postgresql.org/message-id/50E4AAB1.9040902@optionshouse.com, but have not seen any improvement.

Any advice on how to trace what could be causing the change in CPU usage and load average is appreciated.

Our postgres version is:

PostgreSQL 9.2.2 on x86_64-unknown-linux-gnu, compiled by gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3, 64-bit

OS:

Linux ip-10-189-175-25 3.2.0-37-virtual #58-Ubuntu SMP Thu Jan 24 15:48:03 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux

Hardware (this an Amazon Ec2 High memory quadruple extra large instance):

8 core Intel(R) Xeon(R) CPU E5-2665 0 @ 2.40GHz
68 GB RAM
RAID10 with 8 drives using xfs
Drives are EBS with provisioned IOPS, with 1000 iops each

Postgres Configuration:

archive_command = rsync -a %p slave:/var/lib/postgresql/replication_load/%f
archive_mode = on
checkpoint_completion_target = 0.9
checkpoint_segments = 64
checkpoint_timeout = 30min
default_text_search_config = pg_catalog.english
external_pid_file = /var/run/postgresql/9.2-main.pid
lc_messages = en_US.UTF-8
lc_monetary = en_US.UTF-8
lc_numeric = en_US.UTF-8
lc_time = en_US.UTF-8
listen_addresses = *
log_checkpoints=on
log_destination=stderr
log_line_prefix = %t [%p]: [%l-1]
log_min_duration_statement =500
max_connections=300
max_stack_depth=2MB
max_wal_senders=5
shared_buffers=4GB
synchronous_commit=off
unix_socket_directory=/var/run/postgresql
wal_keep_segments=128
wal_level=hot_standby
work_mem=8MB

Thanks,
Dan