I didn't mean to imply that SIGA is not a machine instruction. All I said was that SSCH is a machine instruction and is not a CCW operation.
The following also is evidence that SIGA is a machine instruction which causes an I/O operation to start in the Channel Subsystem, just as will happen with SSCH: http://publib.boulder.ibm.com/infocenter/zos/v1r9/index.jsp?topic=/com.ibm.zos.r9.ieav100/stio.htm This page shows the format of system trace entries for the CSCH, HSCH, ..., SSCH, SIGA, ... trace entries, confirming that SIGA is a machine instruction. It is also mentioned in the Diagnosis Tools and Service Aids book under System Trace but not in the section on GTF. The opcode and some operands are shown on this page: http://www.cbttape.org/~jjaeger/opcodes.html#OSA That's all I know about it. This should give you a good place to start for further research. Bill Fairchild Rocket Softare -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of John Blythe Reid Sent: Thursday, November 04, 2010 12:27 PM To: [email protected] Subject: Re: QDIO question This is the bit that made me think SIGA was a machine instruction: --------------------------Extract from networking on z/OS------------------------------------------------------------- The advantages of using QDIO mode are: --A 20% improvement in performance versus non-QDIO mode --The reduction of system assist processor (SAP) utilization --Improved response time --Server cycle reduction How is this all accomplished? Instead of attaching an OSA-Express card using a channel, and hence utilizing a channel or I/O program (IOP) combined with CCW operations, the OSA-Express card attaches using an STI bus. STI stands for Self-Timed Interface. The OSA-Express card is still connected within the I/O cage, but the STI bus is directly connected to the memory bus of the CPC. What is used instead of a CCW operation to signify that I/O needs to be completed? With an OSA-Express card running in QDIO mode, I/O operations are effected using a signal adapter instruction, or SIGA. The SIGA is still processed by the SAP, similar to the way a CCW is processed by the SAP. However, the SIGA effectively passes a pointer to the data because the data already occupies internal storage. -----------------------End of extract from networking on z/OS------------------------------------------------------------- >From this I assume that a SSCH instruction is issued for a QDIO sub-channel and this will cause one CCW to be executed with a CCW command code of SIGA. Am I on the right track here ? Thanks. Regards, John. ------------------------------ For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
