Re: Patches to get oprofile to work with perfmon2 on amd64

[Stephane E. <er...@hp...>]

Will,

On Wed, Mar 29, 2006 at 09:12:17AM -0500, William Cohen wrote:
> The native OProfile driver on x86-64 and i386 use the NMI. This does 
> allow sampling in IRQ routines. However, need to make sure that the 
> amount of time spent in the NMI handler is limited. Using the NMI 
> routine appears to cause problems on some machines (e.g. laptops where 
> the NMI could happen when the BIOS is doing some power management 
> operation).
> 
> Is there some idea of the overhead in the perfmon2 timer interval and 
> sampling mechanisms?
> 
I maintain some statistics per cpu in /sys/devices/system/cpu/cpu*/perfmon/
Keep in mind that the code has not been optimized at this point.

On 1.5GHz Itanium2, it takes about 800 cycles to record a sample. Knowing 
there is an uncompressible 200 cycles or so to get in and out of the kernel and
to/from C code.

-- 
-Stephane