% PT_QRY_TIME(3)

NAME

pt_qry_time, pt_qry_core_bus_ratio, pt_insn_time, pt_insn_core_bus_ratio, pt_blk_time, pt_blk_core_bus_ratio - query an Intel(R) Processor Trace decoder for timing information

SYNOPSIS

Link with -lipt.

DESCRIPTION

pt_qry_time(), pt_insn_time(), and pt_blk_time() provide the current estimated timestamp count (TSC) value in the unsigned integer variable pointed to by the time argument. The returned value corresponds to what an rdtsc instruction would have returned.

At configurable intervals, Intel PT contains the full, accurate TSC value. Between those intervals, the timestamp count is estimated using a collection of lower-bandwidth packets, the Mini Time Counter (MTC) packet and the Cycle Count Packet (CYC). Depending on the Intel PT configuration, timing can be very precise at the cost of increased bandwidth or less precise but requiring lower bandwidth.

The decoder needs to be calibrated in order to translate Cycle Counter ticks into Core Crystal Clock ticks. Without calibration, CYC packets need to be dropped. The decoder calibrates itself using MTC, CYC, and CBR packets.

To interpret MTC and CYC packets, the decoder needs additional information provided in respective fields in the pt_config structure. Lacking this information, MTC packets may need to be dropped. This will impact the precision of the estimated timestamp count by losing periodic updates and it will impact calibration, which may result in reduced precision for cycle-accurate timing.

The number of dropped MTC and CYC packets gives a rough idea about the quality of the estimated timestamp count. The value of dropped MTC and CYC packets is given in the unsigned integer variables pointed to by the lost_mtc and lost_cyc arguments respectively. If one or both of the arguments is NULL, no information on lost packets is provided for the respective packet type.

pt_qry_core_bus_ratio(), pt_insn_core_bus_ratio(), and pt_blk_core_bus_ratio() give the last known core:bus ratio as provided by the Core Bus Ratio (CBR) Intel PT packet.

RETURN VALUE

All functions return zero on success or a negative pt_error_code enumeration constant in case of an error.

ERRORS

pte_invalid

The decoder or time (pt_qry_time(), pt_insn_time(), and pt_blk_time()) or cbr (pt_qry_core_bus_ratio(), pt_insn_core_bus_ratio(), and pt_blk_core_bus_ratio()) argument is NULL.

pte_no_time

There has not been a TSC packet to provide the full, accurate Time Stamp Count. There may have been MTC or CYC packets, so the provided time may be non-zero. It is zero if there has not been any timing packet yet.

Depending on the Intel PT configuration, TSC packets may not have been enabled. In this case, the time value provides the relative time based on other timing packets.

pte_no_cbr

There has not been a CBR packet to provide the core:bus ratio. The cbr value is undefined in this case.

NOTES

All decoders read ahead. The estimated timestamp count and core:bus ratios correspond to their current decode position, which may be ahead of the trace position that matches the last event, instruction, or block.

The query decoder also provides an estimated timestamp count in the pt_event structure.

SEE ALSO

pt_qry_alloc_decoder(3), pt_qry_free_decoder(3), pt_qry_cond_branch(3), pt_qry_indirect_branch(3), pt_qry_event(3), pt_insn_alloc_decoder(3), pt_insn_free_decoder(3), pt_insn_next(3), pt_blk_alloc_decoder(3), pt_blk_free_decoder(3), pt_blk_next(3)