=================================================== -----Original Message----- From: "Binyamin Dissen" <[EMAIL PROTECTED]> Sent: 7/27/2006 11:40 AM To: "IBM-MAIN@BAMA.UA.EDU" <IBM-MAIN@BAMA.UA.EDU> Subject: Re: Doing a LM of two words on a double word bounday - is it serialized?
On Thu, 27 Jul 2006 17:21:00 +0000 "Jeffrey D. Smith" <[EMAIL PROTECTED]> wrote: /snip/ :>All CPUs that are fetching/storing must use the same alignment :>and the same serialization mechanism. For updating, they must :>all use CS/CDS/CSG/CDSG, or they must all use PLO with R1 pointing :>at the same lock token (I just use the list header address for R1). :>PLO is designed for discontiguous fetch/store. If it just happens :>that two words are adjacent in the same double word, that won't :>assure an 8-byte concurrent store as viewed by other CPU. It will :>look like two 4-byte concurrent stores separated in time. The PLO :>compare-swap-single/double/triple-store performs the compare :>first and the swap last. All of the accesses performed by PLO :>appear to other CPU to be separated in time. PLO simply uses a :>"red light/green light" hardware semaphore to delay other CPU :>(also using PLO) from accessing the operands. In other words, are you saying in the case above that the LM can get inconsistent results? That L/PLO-CL is required? -- Binyamin Dissen <[EMAIL PROTECTED]> =================================================== You can read the PoPs appendix that describes using L with PLO. In general, the serial number is fetched with L, then it is compared with multiple PLO-CL to get the other discontiguous fields. If the compare is unequal, then branch back to the first PLO-CL and start over. If you are using LM to peek at two adjacent fields which are updated by PLO-CSST, that will very probably fail because the LM is double-word concurrent and the PLO is single word concurrent (the single words are accessed at different times). Jeffrey D. Smith Farsight Systems Corporation 24 BURLINGTON DR LONGMONT, CO 80501 303-774-9381 direct 303-709-8153 cell 303-484-6170 fax ---------------------------------------------------------------------- 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
