Little need for dual path now, unless you are writing for a very specialized
market. All current releases of z/OS demand a machine of at least a recent
enough vintage as to support STCKF.
Charles
-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf
Of Gord Tomlin
Sent: Tuesday, March 12, 2019 9:55 AM
To: [email protected]
Subject: Re: STCKE faster than STCK! (was: instruction clock speed)
On 2019-03-12 12:32, Charles Mills wrote:
> Yes, STCK guarantees a unique value. If the clock has not ticked since the
> last STCK, the CPU has no choice but to spin until it does. STCKE has smaller
> "ticks" and so has less of (or no) need for a spin. STCKF is just like STCK
> except that it does not guarantee a unique value, and so there is never a
> need to spin, and so it is a "fast" instruction. If all you need is "the
> time" and not a unique timestamp, always use STCKF. It is a one-character
> change to your program and may speed it up considerably.
>
> Charles
Going back in time a bit, we were advised by IBM that the performance of
the STCKF instruction is sufficiently better than that of the STCK
instruction that it is worthwhile to write dual-pathed code that uses
STCKF instead of STCK if the machine supports the use of STCKF.
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