The Itanium 2 TLB implementation is split for instructions and data, with two levels for each. The first level only maps 4K pages. Thus, the miss rate (per sec/per kinst) might be quite high. The second level supports large pages and is backed up by hardware that automatically inserts the required translation if it is found to be the head element on the page table list. The hardware insertion hardware does not traverse the page table list. If the required translation is not the first translation on the page list, it will trap to software to perform the update.

If you use this event set, the default is to make the measurements irrespective of CPU operating state (that is, user, system, or interrupt states). By default, the idle state is not included in the measurement. You can use command-line options to limit the scope of the measurement. Specifically, you can:

•Limit measurement to a specific privilege level: -m event_set[:alluserkernel]

•Include idle: --exclude-idle False

•Exclude the interruption state: --measure-on-interrupts off

•Only measure the interruption state: --measure-on-interrupts only

The event per kinst (event per 1000 instructions) metrics are computed using all instructions retired. This includes nops, predicated off instructions, failed speculation and instructions and associated recovery code as well as the architecturally visible instruction. You can eliminate idle loops effects by using the command-line option --exclude-idle True (which is the default). The effects of failed speculative operations and TLB misses cannot be directly eliminated, but you can get an estimate of the impact of events from the cspec, dspec, and tlb event sets. You can use the cpi event set to obtain the fraction of all instructions retired that have an architecturally visible result, except for predicated off branches, which are counted as useful instructions (non-taken branch) by the Itanium 2 PMU.

Metrics Available from this Measurement

The following metrics are available from this event set. These descriptions do not take into account any command-line options you might use.

The metrics are:

•I1TLB Misses Per Sec

This is the number of level 1 ITLB misses per second. This level of the ITLB only operates with 4K pages. Thus, its miss rate will be high, but it is normally the case that any required translation would be provided by the level 2 ITLB in three cycles.

•I2TLB Misses Per Sec

This is the number of level 2 ITLB misses per second. A miss at this level will attempt to be serviced by the hardware page walker (HPW). If the required translation is at the head of the hash table, the hardware automatically inserts the translation into the I2TLB. If the required translation is not the head element, a trap will be taken to the software TLB handler to perform the requisite update.

•D1TLB Misses Per Sec

This is the number of level 1 DTLB misses per second. This level of the DTLB only operates on 4K pages. Thus, its miss rate will be high, but it is normally the case that any required translation would be provided by the level 2 DTLB in three cycles.

•D2TLB Misses Per Sec

This is the number of level 2 DTLB misses per second. A miss at this level will attempt to be serviced by the HPW. If the required translation is at the head of the hash table, the hardware automatically inserts the translation into the DTLB. If the required translation is not the head element, a trap will be taken to the software TLB handler to perform the requisite update.

tlb Event Set 251