Paul Mackerras wrote:
On Wed, Feb 10, 2010 at 06:06:10PM -0600, Scott Wood wrote:
Paul Mackerras wrote:
Some limitations:
- No threshold support -- need to figure out how to represent it in
the event struct from userspace.
What does "threshold support" mean in this context? Does it mean
something different from getting an interrupt after N events have been
counted? Or does it mean counting instances where something takes
longer than a specific number of cycles?
The latter.
OK. I handled that on classic by using some extra high bits in the
event config for the threshold value.
OK.
If you have a single threshold
value in hardware but more than one event that uses that threshold
value, then you will need to add a constraint that all threshold
events have to specify the same threshold.
There's a separate threshold for each counter.
So, it sounds like you have a class of events which are the
thresholding events, and two constraints:
* at most two events in the thresholding event class
* at most four events in total
Are there other constraints? Apart from the thresholding events, can
any event go on any counter, or can some events only be counted on one
particular counter?
No, those are the only constraints.
If your constraints are just the two listed above (<= 2 threshold
events, <= 4 events total), then doing it the obvious straightforward
way is fine. If there are other constraints as well, such as certain
events only being available on one specific PMC, then you should
consider reusing the constraint checking machinery from ppc64.
I'll stick with the straightforward approach then. If future chips have
more complicated constraints we can revisit using the more general scheme.
-Scott
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