Compaq EV68A ProfileMe Mode Programming Guidelines, This input counts Mbox replay traps

Performance Counter Support

6.10.2.3 Aggregate Counting Mode Description

6.10.2.3.1 Cycle counting

Counts cycles.

PCTR0 is incremented by the number of cycles counted, that is, 1.

6.10.2.3.2 Retired instructions cycles

PCTR0 is incremented by up to 8 retired instructions per cycle when enabled via

I_CTL[PCT0_EN] and either I_CTL[SPCE] or PCTX[PPCE]. On overflow, an inter- rupt is triggered as ISUM[PC0] if enabled via IER_CM[PCEN0].

The 21264/EV68A can retire up to 11 instructions per cycle, which exceeds PCTR0's maximum increment of 8 per cycle. However, no retires go uncounted because the 21264/EV68A cannot sustain 11 retires per cycle, and the 21264/EV68A corrects PCTR0 in subsequent cycles.

A squashed instruction does not count as a retire.

6.10.2.3.3 Bcache miss or long latency probes cycles

This input counts the number of times the Bcache result was a miss.

Essentially, a long latency probe is a data request from other processes that cause Bcache misses in a system.

This count is phase shifted three cycles early and thus includes events that occurred three cycles before the start and before the end of the ProfileMe window.

6.10.2.3.4 Mbox replay traps cycles

This input counts Mbox replay traps.

6.10.2.4 Counter Modes for Aggregate Mode

Table 6–11shows the counter modes that are used with Aggregate mode.

Table 6–11 Aggregate Mode Performance Counter IPR Input Select Fields

SL0[4]	SL1[3:2]	PCTR0	PCTR1
0	00	Retired instructions	Cycle counting
0	01	Cycle counting	Not defined
0	10	Retired instructions	Bcache miss or long latency probes
0	11	Cycle counting	Mbox replay traps

6.10.3 ProfileMe Mode Programming Guidelines

Use the following information to program counters in ProfileMe mode.

6.10.3.1 ProfileMe Mode Precautions

Squashed NOPs count as valid fetched instructions.

Counter 1 must be explicitly cleared in the trap handler before each data collection.

6–20Privileged Architecture Library Code 21264/EV68A Hardware Reference Manual