> > Are there more context switching overheads when running 32bit programs on
> > a 64bit kernel?
>
> Should be nearly the same in theory, no. This means 32bit programs use %gs
> as thread register which is a bit more costly to switch because
> the kernel uses it internally too, but the difference should be less
> than that.
>
> I suspect your program is more testing the locks anyways, perhaps
> there is some other difference in the glibc. e.g. 32bit glibc compiled
> for pre 686 CPUs has slower locks.
>
> oprofile might provide more clue where the overhead is.
>
> -Andi

I ran the 32 bit and 64 bit versions in a loop for good amount of time and 
captured oprofile report for vmlinux after each run. For the 32 bit runs the 
top 5 are - (Also attached are complete reports after 32 bit and 64 bit runs)

samples  %        symbol name
20820    11.5424  copy_user_generic_c
12990     7.2015  ia32_syscall
10131     5.6165  gs_change
9053      5.0189  __dequeue_signal
7494      4.1546  find_pid

For the 64 bit run top 5 are -
samples  %        symbol name
10604     8.1075  system_call
8497      6.4965  __switch_to
8041      6.1479  do_signal
7712      5.8963  schedule
6538      4.9987  __dequeue_signal

I am yet to interpret/analyze the above...

Parag