Linux – How to find out where a file is physically located on the disk (block numbers)

This is an obscure question, I know. I'm trying to do some performance testing of some disks on a Linux box. I'm getting some inconsistent results, running the same test on the same disk. I know that disks have different performance depending on which part of the disk is being accessed. In particular, reads and writes to the outside of the disk have much higher throughput than reads and writes to the inside part of the disk, due to near-constant data density and constant rotational speed.

I'd like to see if my inconsistencies can be attributed to this geometry-induced variance in throughput. Is it possible, using existing tools, to find out where on the disk a file has been placed?

If not, I suppose I can write something to directly seek, read, and write to the device file itself, bypassing (and destroying) the filesystem, but I'm hoping to avoid that. I'm currently using ext4 on a 3.0 kernel (Arch Linux, if it matters), but I'm interested in techniques for other filesystems as well.