There is a potentially meaningful performance hit only if the load module /
program object is marked refreshable. For the non-refreshable case, the
one--time performance hist (the first time ST R15,PTR is executed) is trivial
compared to the potential cost of getting the called program address.
Don't mark such code refreshable and you will be fine.
This is an old, old technique used in probably thousands or more of "dynamic
call" assembler stub programs. Yes there are modern, reentrant and refreshable
techniques now - name/token pair comes to mind - but they are not without their
own cost in CPU time.
I wouldn't call the technique ugly, just necessary and (relatively) efficient.
If it ain't broke, don't fix it.
Peter
-----Original Message-----
From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> On Behalf Of
Seymour J Metz
Sent: Monday, February 8, 2021 1:04 PM
To: IBM-MAIN@LISTSERV.UA.EDU
Subject: Re: LINK vs LOAD/CALL
EXTERNAL EMAIL
My original code had the DC after everything else. But if the DC is too close
to the code, then there will be a performance hit. Even if not, it's ugly. Not
everything that is possible is desirable.
--
________________________________________
From: IBM Mainframe Discussion List [IBM-MAIN@LISTSERV.UA.EDU] on behalf of
Gibney, Dave [gib...@wsu.edu]
Sent: Monday, February 8, 2021 12:38 PM
To: IBM-MAIN@LISTSERV.UA.EDU
Subject: Re: LINK vs LOAD/CALL
Would
> This is refreshable, and even runs on S/360
PTR DC A(0)
label L R15,PTR
LTR R15,R15
BNZ CALLIT
... ... Code that always
leaves the same value in R15
ST R15,PTR
CALLIT BALR R14,R15
Still incur cache flush?
> -----Original Message-----
> From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> On
> Behalf Of Seymour J Metz
> Sent: Sunday, February 07, 2021 6:38 PM
> To: IBM-MAIN@LISTSERV.UA.EDU
> Subject: Re: LINK vs LOAD/CALL
>
> This is refreshable, and even runs on S/360
>
> L R15,PTR
> LTR R15,R15
> BNZ CALLIT
> ... ... Code that always
> leaves the same value in R15
> ST R15,PTR
> CALLIT BALR R14,R15
> ...
> PTR DC A(0)
>
> This is reentrant, and requires at least S/370
>
> RETRY L R1,COUNTER
> LA R0,1(,R1)
> CS R1,,R0,COUNTER
> BNE RETRY
> ...
> COUNTER DC F'0'
>
> I would consider either to be bad form.
--
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