PLO? MVCL? Or do you mean specifically a slow instruction to zero a register?
-- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> on behalf of Christopher Y. Blaicher <cblaic...@syncsort.com> Sent: Thursday, March 7, 2019 10:34 AM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: instruction clock speed OK. What runs 250 times slower than a LG instruction? Chris Blaicher Technical Architect Syncsort, Inc. -----Original Message----- From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf Of Ed Jaffe Sent: Thursday, March 7, 2019 1:38 AM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: instruction clock speed On 3/6/2019 8:18 PM, Charles Mills wrote: > My imperfect model is that main storage is the new disk. Figure that > instructions take no time at all and memory accesses take forever. Of course, you need to pay attention to cache effects -- *especially* to avoid sharing R/W cache lines across CPs. But, that doesn't mean you should completely ignore instruction speed. Here are three instructions guaranteed to produce the identical result: XGR R0,R0 LGHI R0,0 MGHI R0,0 As you might expect, the MGHI runs _significantly_ slower than the other two. XGR and LGHI are similar, but LGHI is the only one of the three that won't slow down to set the CC. Which would you use? (A silly example since no sane person would think to use a multiply to load a zero... LOL) Using our benchmark program, we know some extremely helpful things about the performance of significantly more complex instructions and we've become aware of some that are surprisingly slow. For example, what do you imagine is the performance difference between doing LMH/LM vs an LMD -- I can tell you it's so significant that you will try very hard to never, ever use LMD if you can help it! (Never use it in commonly-used register unstacking code like we stupidly did at one time...) Likewise, if you knew a seemingly-innocent instruction ran 250 times slower than a simple LG, would you try to avoid using it wherever you could? (We avoid that one in high-performing code.) -- Phoenix Software International Edward E. Jaffe 831 Parkview Drive North El Segundo, CA 90245 https://secure-web.cisco.com/1rWe-cfovUc4rY3NC9YIPxe4Gr2lpjjZoZx7IY6pRFJdloG9ZveHRKJzXe2EJtJ9EbxXNvh_0wPJOBD3H3TnAGB3Xs8R4aB4gtvKChhuB8obgsSW_E65U9hl20n5ct_i4RDrM_pq2X_fcI9J2sXMqOQ3EN4VcnT_1i5t2_GzkHkfgoJVpl3j1miBV1UxtYtqo8307yaOs_X9gh9FwOaXwDbPPVnAlXkOEVPt17aphwJse8FFVzQwC6OpMNMnY6ADwOJcTpoN4-esdyqCHWXtDQ-iugDUxZb-t09PHv9eC0IxfUbF4WJ_nio81tdJLAv_MRcVNAdd9T1sGwIcul3x7mVAYjyZSQuuy3sj4UvSoFbRuoWILZedB2NzaHxRYEWZgPF9jRJrsk0MDQz9pOzW91H1PNHx_wL0CuI2fnvBAIr4gf6KEQ4Sj27NEbP22ICOa/https%3A%2F%2Fwww.phoenixsoftware.com%2F -------------------------------------------------------------------------------- This e-mail message, including any attachments, appended messages and the information contained therein, is for the sole use of the intended recipient(s). If you are not an intended recipient or have otherwise received this email message in error, any use, dissemination, distribution, review, storage or copying of this e-mail message and the information contained therein is strictly prohibited. If you are not an intended recipient, please contact the sender by reply e-mail and destroy all copies of this email message and do not otherwise utilize or retain this email message or any or all of the information contained therein. Although this email message and any attachments or appended messages are believed to be free of any virus or other defect that might affect any computer system into which it is received and opened, it is the responsibility of the recipient to ensure that it is virus free and no responsibility is accepted by the sender for any loss or damage arising in any way from its opening or use. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
