PostgreSQL performance on 64 bit as compared to 32 bit

Hello All,
 
We are migrating our product from 32 bit CentOS version 5.0 (kernel 2.6.18) to 64 bit CentOS version 6.0 (kernel 2.6.32)
So we decided to upgrade the PostgreSQL version from 8.2.2 to 9.0.4
 
We are compiling the PostgreSQL source on our build machine to create an RPM before using it in our product.
 
The issue we have noticed is the 9.0.4 (64 bit) version of PostgreSQL has slower performance as compared to 8.2.2 (32 bit) version on an identical hardware.
 
To investigate further we tried monitoring the PostgreSQL process using strace and found that the earlier version of PostgreSQL was using _llseek() system call whereas the later version is using lseek() system call.
 
Will this impact the PostgreSQL performance? When the timing is on we found every query executed on 9.0.4 was taking longer than the query executed on 8.2.2
 
Please guide me what should I see while compiling the PostgreSQL 9.0.4 version to improve its performance.
 
Thank you,
Umesh