Hi,

I did some trials based on some reading on millicode instructions, and please find my observations below:

Observation-1 (Compiler listing based)

Some examples of millicode instructions in z/OS High Level Assembler are MVCL and CLCL.

MVC versus MVCL

Field length is <= 256 bytes       àCompiler choses MVC (Maximum that MVC can handle)

Field length is > 256 bytes         àCompiler choses MVCL

Compiler uses a similar judgment for IF checks also (CLC versus CLCL), and also for the verbs like INITIALIZE (MVC versus MVCL)

 

WORKING-STORAGE SECTION.                   

01 WS-VAR1   PIC X(255)       VALUE SPACE.       

01 WS-VAR2   PIC X(255)       VALUE SPACE.      

01 WS-VAR3   PIC X(4000)      VALUE SPACE.      

01 WS-VAR4   PIC X(4000)      VALUE SPACE.      

PROCEDURE DIVISION.                        

    MOVE WS-VAR1 TO WS-VAR2                

    MOVE WS-VAR3 TO WS-VAR4                

 

===================================

000011  MOVE                                                                

   000364  D2FE 8100 8000          MVC   256(255,8),0(8)         WS-VAR2    ßCompiler converted this to MVC

000012  MOVE                                                               

   00036A  5840 9130               L     4,304(0,9)              BLW=1       

   00036E  4120 41A0               LA    2,416(0,4)              WS-VAR4     

   000372  4130 0FA0               LA    3,4000(0,0)                         

   000376  4160 8200               LA    6,512(0,8)              WS-VAR3     

   00037A  5870 A010               L     7,16(0,10)              PGMLIT AT +8

   00037E  0E26                    MVCL  2,6                                ßCompiler converted this to MVCL

 

Observation-2 (Test volume based)

Note: I checked with my system admin team and they were not sure if we have the necessary firmware/hardware in place to handle millicode instructions in an optimized manner. As per my understanding, the performance of millicode instructions would be very low when the additional firmware/hardware is not in place (I think it's separately licensed).

 

Original:

WORKING-STORAGE SECTION.                

01 WS-VAR3   PIC X(4000) VALUE SPACE.   

01 WS-VAR4   PIC X(4000) VALUE SPACE.   

PROCEDURE DIVISION.                     

    PERFORM 10000000  TIMES              

       MOVE WS-VAR3 TO WS-VAR4          

    END-PERFORM                         

    STOP RUN.                         

 

Modified:

WORKING-STORAGE SECTION.                    

01 WS-VAR3.                                 

   05 WS-VAR31    PIC X(256) VALUE SPACE.      

   05 WS-VAR32    PIC X(256) VALUE SPACE.      

   05 WS-VAR33    PIC X(256) VALUE SPACE.      

   05 WS-VAR34    PIC X(256) VALUE SPACE.      

   05 WS-VAR35    PIC X(256) VALUE SPACE.      

   05 WS-VAR36    PIC X(256) VALUE SPACE.      

   05 WS-VAR37    PIC X(256) VALUE SPACE.      

   05 WS-VAR38    PIC X(256) VALUE SPACE.      

   05 WS-VAR39    PIC X(256) VALUE SPACE.      

   05 WS-VAR310   PIC X(256) VALUE SPACE.     

   05 WS-VAR311   PIC X(256) VALUE SPACE.     

   05 WS-VAR312   PIC X(256) VALUE SPACE.     

   05 WS-VAR313   PIC X(256) VALUE SPACE.     

   05 WS-VAR314   PIC X(256) VALUE SPACE.     

   05 WS-VAR315   PIC X(256) VALUE SPACE.     

   05 WS-VAR316   PIC X(160) VALUE SPACE.     

01 WS-VAR4.                                 

   05 WS-VAR41    PIC X(256) VALUE SPACE.      

   05 WS-VAR42    PIC X(256) VALUE SPACE.         

   05 WS-VAR43    PIC X(256) VALUE SPACE.         

   05 WS-VAR44    PIC X(256) VALUE SPACE.         

   05 WS-VAR45    PIC X(256) VALUE SPACE.         

   05 WS-VAR46    PIC X(256) VALUE SPACE.         

   05 WS-VAR47    PIC X(256) VALUE SPACE.         

   05 WS-VAR48    PIC X(256) VALUE SPACE.         

   05 WS-VAR49    PIC X(256) VALUE SPACE.         

   05 WS-VAR410   PIC X(256) VALUE SPACE.        

   05 WS-VAR411   PIC X(256) VALUE SPACE.        

   05 WS-VAR412   PIC X(256) VALUE SPACE.        

   05 WS-VAR413   PIC X(256) VALUE SPACE.        

   05 WS-VAR414   PIC X(256) VALUE SPACE.        

   05 WS-VAR415   PIC X(256) VALUE SPACE.        

   05 WS-VAR416   PIC X(160) VALUE SPACE.        

  PROCEDURE DIVISION.                            

      PERFORM 10000000 TIMES                      

              MOVE WS-VAR31  TO WS-VAR41       

              MOVE WS-VAR32  TO WS-VAR42       

              MOVE WS-VAR33  TO WS-VAR43       

              MOVE WS-VAR34  TO WS-VAR44       

              MOVE WS-VAR35  TO WS-VAR45        

              MOVE WS-VAR36  TO WS-VAR46       

              MOVE WS-VAR37  TO WS-VAR47       

              MOVE WS-VAR38  TO WS-VAR48       

              MOVE WS-VAR39  TO WS-VAR49       

              MOVE WS-VAR310 TO WS-VAR410      

              MOVE WS-VAR311 TO WS-VAR411      

              MOVE WS-VAR312 TO WS-VAR412      

              MOVE WS-VAR313 TO WS-VAR413      

              MOVE WS-VAR314 TO WS-VAR414      

              MOVE WS-VAR315 TO WS-VAR415      

              MOVE WS-VAR316 TO WS-VAR416

      END-PERFORM

      STOP RUN.     

 

	SINGLE MOVE
	No. of performs	TOTAL TCB CPU TIME	TOTAL ELAPSED TIME	Execution time (Mins)	% Reduction in execution time
Original	10000000	0.03	0	0.03
Modified	10000000	0.02	0	0.02	33.33
Original	20000000	0.06	0	0.06
Modified	20000000	0.04	0	0.04	33.33
Original	30000000	0.09	0	0.09
Modified	30000000	0.06	0	0.06	33.33
Original	40000000	0.12	0.1	0.12
Modified	40000000	0.08	0	0.08	33.33
Original	50000000	0.15	0.1	0.16
Modified	50000000	0.1	0	0.1	37.50
	10 MOVES
Original	1000000	0.03	0	0.03
Modified	1000000	0.02	0	0.02	33.33
Original	2000000	0.06	0	0.06
Modified	2000000	0.04	0	0.04	33.33
Original	3000000	0.09	0	0.09
Modified	3000000	0.06	0	0.06	33.33

 

My query:

Are such millicode instructions worth looking at from the performance optimization point of view for COBOL programs? If so, how can we identify if the necessary firmware is in place or not? What are the other related considerations?

 

Thanks,
Anitha.

I don't know anything about the hardware itself, but I can point out that in COBOL V5.2, you'll get very different code for larger moves. Depending on the number of instructions that will be generated and some other conditions, we may generate a series of MVCs, use a single MVC in a loop, or use an EX to execute a single MVC.

Well, it looks like it'd save you 1/3 *of the CPU used for a big MOVE*.

The impact this has a on the resource-usage of any given program "depends".

If you do the split of the fields, you have to get everything correct (running faster but not working is no good). If you can wait for V5+, you won't need to do anything.

Unless you can do the best thing. Which is not to do the MOVE at all.

Many, many MOVEs (implicit or explicit) to/from the FILE SECTION are unnecessary. less so but happens with the LINKAGE SECTION. With those, you make the MOVE 100% faster, but again you have to get it right.

Do you have particular performance problems, or you are just looking for tips? Unfortunately a lot of people believe that the FILE and LINKAGE SECTIONs are somehow "unsafe" and you should "get the data out of them as soon as possible".  It's plain flat wrong, but many believe. Instead "Do you really need to MOVE that data?".