On Tue, 2013-04-30 at 12:27 -0400, Vince Weaver wrote:
> On Tue, 30 Apr 2013, Carl E. Love wrote:
>
> > The Power 7 processor has four programmable counters and two fixed counters.
> > Currently, the codes returned for PM_RUN_INST_CMPL and PM_RUN_CYC are for
> > the programmable counters. This patch changes the returned code to the
> > fixed counter code thus freeing up the programmable counters for other
> > events.
>
> Instead of replacing the definition, would it make sense to just add an
> additional definition so there is two events listed, one fixed, one not?
> That way a user could pick which one they wanted?
>
> I guess on POWER it might not matter, but at least on recent Intel chips
> it would be nice if we could specify the difference as it turns out the
> fixed vs programmable events have subtle differences and it's hard to test
> this as it's impossible to specify one vs the other.
>
The events are identical for the two counters. In general, I don't
think the users know that there are two types of counters. So, if we
gave them both values and the user picked the value for the programmable
counter for use in perf along with say four additional events then perf
would have to multiplex the five events on four programmable counters.
But if they were to pick the event for the fixed counter, perf would not
multiplex the events. Not sure how you get a tool like event2raw to
give both codes plus the explanation about programmable and fixed
counters so the user would know the ramifications of choosing one versus
the other.
We don't see any use scenario where using the event code in the
programmable counter would be needed or preferable to using the fixed
counter as the results are identical. So, it seems better to have one
event for the fixed counter so the user doesn't have to know the details
of fixed versus programmable counters or inadvertently have events
multiplexed when it is not necessary.
Does that seem reasonable?
Carl Love
------------------------------------------------------------------------------
Introducing AppDynamics Lite, a free troubleshooting tool for Java/.NET
Get 100% visibility into your production application - at no cost.
Code-level diagnostics for performance bottlenecks with <2% overhead
Download for free and get started troubleshooting in minutes.
http://p.sf.net/sfu/appdyn_d2d_ap1
_______________________________________________
perfmon2-devel mailing list
perfmon2-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
