Red Hat Enterprise Linux 5 Administration Unleashed

OProfile 451The performance monitoring hardware on the processor contains counters, and thenumber of counters available depends on the processor type. The number of events thatcan be monitored by OProfile depends on the number of counters, and in some cases,certain events can only be monitored by a specific counter. If the timer interrupt is usedby OProfile, the number of counters is 1.Execute the ophelp command (equivalent to opcontrol --list-events) to display a listof available events for the system’s processor type. The ophelp output is processor-specificand varies from system to system. If specific counters must be used for the event, they arelisted with the event. For example, Listing 22.2 shows the MEMORY_COMPLETE event for ani386/p4 processor, which must be profiled with counters 2 and 6.22LISTING 22.2Counter-Specific EventMEMORY_COMPLETE: (counter: 2, 6)completed split (min count: 3000)Unit masks (default 0x3)----------0x01: load split completed, excluding UC/WC loads0x02: any split stores completed0x04: uncacheable load split completed0x08: uncacheable store split completeIf any counter can be used, the keyword all is used for the counter numbers as shown inListing 22.3 for the MEMORY_DISAMBIGUATION event on an i386/core2 processor.LISTING 22.3Event That Can Profiled with All CountersMEMORY_DISAMBIGUATION: (counter: all)Memory disambiguation reset cycles. (min count: 1000)Unit masks (default 0x1)----------0x01: RESET Memory disambiguation reset cycles.0x02: SUCCESS Number of loads that were successfully disambiguated.For each counter available, the following command can be used to associate an event with it:opcontrol –event=:::: \--separate=The arguments for the command are as follows:. --event= sets which event to profile. Use the ophelp command to list availableevents for the system along with brief descriptions for each.. is the number of events between sampling. The lower the number,the more samples taken. Use caution when setting the sample rate. If it is set toolow, sampling might occur too frequently and slow down the system or make thesystem appear unresponsive.