pcd_width

[Rui Paulo]

I'm trying to find the meaning of this field. What's it for?

BTW, XScale now prints something:

hwpmc: XSCALE/2/48/0x1ff<INT,USR,SYS,EDG,THR,REA,WRI,INV,QUA>

# pmccontrol -L
XSCALE
IC_FETCH
IC_MISS
DATA_DEPENDENCY_STALL
ITLB_MISS
DTLB_MISS
BRANCH_EXECUTED
BRANCH_MISPRED
INSTR_EXECUTED
DC_FULL_CYCLE
DC_FULL_CONTIG
DC_ACCESS
DC_MISS
DC_WRITEBACK
PC_CHANGE

--
Rui Paulo

[Joseph Koshy]

> I'm trying to find the meaning of this field. What's it for?

It records the number of active bits in a PMC of a given class.

E.g., early Intel PMCs had an effective width of 40 bits (IIRC), but
were read/written using 64 bit operations. The current crop of Intel
PMCs have variable widths, depending on the CPU implementation; the
exact width on a CPU has to be queried at run time.

> BTW, XScale now prints something:
>
> hwpmc: XSCALE/2/48/0x1ff<INT,USR,SYS,EDG,THR,REA,WRI,INV,QUA>
>
> # pmccontrol -L
> XSCALE
> IC_FETCH
> IC_MISS
> DATA_DEPENDENCY_STALL
> ITLB_MISS
> DTLB_MISS
> BRANCH_EXECUTED
> BRANCH_MISPRED
> INSTR_EXECUTED
> DC_FULL_CYCLE
> DC_FULL_CONTIG
> DC_ACCESS
> DC_MISS
> DC_WRITEBACK
> PC_CHANGE

Very cool :).

Koshy