On Sun, 10 Sep 2017 23:56:21 +0100 David W Noon <0000013a910fd252-dmarc-requ...@listserv.ua.edu> wrote:
:>On Sun, 10 Sep 2017 09:40:09 -0700, Charles Mills (charl...@mcn.org) :>wrote about "CSST question" (in <0b3a01d32a53$776116a0$662343e0$@mcn.org>): :>> Is that saying that there is a chance that another CPU might observe a :>> condition in which the store of the first operand had occurred, but the :>> store of the second operand had not? My understanding from earlier :>> paragraphs was that CSST happened "all at once" from the point of view of :>> other CPUs. Was I mistaken? :>My reading of PoOps is that CSST is guaranteed to be atomic, just like :>the other instructions in the compare-and-swap family. So your first :>understanding is correct. My understanding is only block-concurrent operations are seen as atomic by other processors, i.e., if one CPU is storing a fullword while another CPU is fetching it, the results of the fetch will be either the original value or the new value but never a combination of some bits/bytes or the original and some bits/bytes of the new. Same with two processes storing - the result will be either the value from CPUA or the value from CPUB - never a combination. As CSST works on separate "blocks" I don't see how this is possible. I don't know if channels are block concurrent or not. -- Binyamin Dissen <bdis...@dissensoftware.com> http://www.dissensoftware.com Director, Dissen Software, Bar & Grill - Israel Should you use the mailblocks package and expect a response from me, you should preauthorize the dissensoftware.com domain. I very rarely bother responding to challenge/response systems, especially those from irresponsible companies. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
