jffs zlib tuning

Tom Sylla tsylla at gmail.com
Wed Jan 9 12:49:39 EST 2008

On Jan 9, 2008 10:51 AM, Jordan Crouse <jordan.crouse at amd.com> wrote:
> We can't use NMI, because we have no mechanism for causing the NMIs.
> Modern processors such as the k8 use registers called event counters
> to count a number of events between sample periods (events being some
> processor quality like "number of instructions executed" or "number of
> cache misses").  These event counters can be set up in such a way that
> they cause a NMI when the counter rolls over.  This is how oprofile
> takes advantage of the silicon.  The kicker is that even though the Geode
> has event counters, we cannot set them up to cause a NMI.  So, with that
> mechanism lost, we're stuck with the timer tick.
> This has been discussed several times over the lifetime of the project - you
> can go back over the archives of the list and see our past conclusions
> on this matter.

There is still the possibility of using the MFGPT block in 5536 to
cause periodic NMIs. That would be similar to oprofile's RTC or timer
interrupt mode, but with support to profile interrupt handler code,
and pretty-good granularity (14MHz-based)

The perfmon-rollover style (not available on LX) is certainly the best
way to do something like oprofile, but if you can make periodic NMIs
fast enough, you should be able to get pretty close to similar

This completely new oprofile mode would be very specific to
GX/LX/5536, but it would improve oprofile usefulness if someone wants
to make the (pretty large) effort.

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