Thanks a lot, Bill. That was the implication of what I'd read, that an instruction called SIGA, did the I/O. They didn't use the word 'command' as would normally be used with a CCW. There's also this diagram that shows that it's quite a different flow:
[image: Non-QDIO versus QDIO data paths] Regards, John. On 4 November 2010 20:04, Bill Fairchild <[email protected]> wrote: > 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 > -- John Blythe Reid, Técnico de Sistemas de z/OS y de Sistemas Transaccionales, Barcelona, España. ---------------------------------------------------------------------- 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
