5 Replies
      Latest reply on Mar 5, 2019 3:32 PM by cwoolf
      jiepan Level 1 Level 1 (0 points)

        I am finding bottlenecks in my app on iPhone XS, and for FIXED_INSTRUCTIONS and FIXED_CYCLES events,

        tooltips is not shown when mouse over the event item, I want to know, what's the meaning of those two events?

        and what's the meaning of "FIXED"? further more, where can I get the detail explanation for each event?

        and for SYNC_DC_STORE_MISS, the tooltips is "counts the number of retired load micro-operations that missed  in the L1D-cache"

        seems it's not correct? Thanks!

        • Re: PMC events meaning
          cwoolf Apple Staff Apple Staff (40 points)

          The instrument is data driven based on files we receive from the CPU architecture teams.  If you think a description is incorrect for a given counter, then please file a bug report (bugreport.apple.com) with that counter and device in question, and we can fix up the database.


          Most CPUs have a limited number of counter registers that can be programmed (configured) to count the events you see in that list.  So while there are hundreds of possible events, you don't have hundreds of programmable registers to count them, so you're limited to however many the hardware supports each recording you take in Instruments.  You can choose a different set of events for the next run, but the number of events you can record depends on how many programmable registers the CPU has.  The FIXED events, however, have dedicated registers associated with them, so they don't count toward your register budget when configuring the instrument.  So "FIXED_INSTRUCTIONS" is just the count of instructions executed, but it's held in one of these non-programmable registers so it's more or less free to record.