Hey, Jon, On Tue, Jul 15, 2008 at 11:15 AM, Jon Haslam <[EMAIL PROTECTED]> wrote: > Hi Chad, > >>> >>> Only one of cpustat and DTrace may use the counter hardware at any one >>> time. >>> Ownership of the counters is given on a first-come, first-served basis. >> >> I'm curious, how does DTrace interact with DTrace in this situation? >> Specifically, if two DTrace invocations (either separate D scripts or >> even two clauses in the same D script) specify the same hardware >> counter in a probe, will they both see (effectively) the same data, or >> will the first invocation be the only one to see useful data? > > > The key thing to remember here is that a probename encodes > everything needed to program the performance counter hardware up. > Therefore, if you have two probes with the same event name but a > different mode or event frequency then it is two different hardware > configurations. If the hardware you're on can't tell which > counter overflowed in the face of multiple active counters (like AMD > or UltraSPARC) then I only allow a single enabling. > > For example, a script that attempts to enable 'cpc:::IC_miss-user-10000' > and 'cpc:::IC_miss-kernel-10000' on an AMD box will succeed for the > first enabling but fail the second and the consumer will exit: > > # dtrace -n 'cpc:::IC_miss-user-10000' -n 'cpc:::IC_miss-kernel-10000' > dtrace: description 'cpc:::IC_miss-user-10000' matched 1 probe > dtrace: failed to enable 'cpc:::IC_miss-kernel-10000': Failed to enable > probe > # > > > I tried to communicate this in section "B3 - Probe Availability". > Give it another read and let me know if it needs improving at all > (or if the above wasn't an correct understanding of your question!).
Okay, this makes sense. On a closer reading of section "B3 - Probe Availability", I can see that the information is there, it just wasn't clear on the first pass. The example you give above makes it very clear, both the case that you're describing and the failure mode, so I might suggest adding that example to that section for clarity. Thanks, Chad _______________________________________________ dtrace-discuss mailing list [email protected]
