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Revision 1.2 / (download) - annotate - [select for diffs], Sat Apr 9 23:32:51 2022 UTC (9 months, 4 weeks ago) by riastradh
Branch: MAIN
CVS Tags: netbsd-10-base,
netbsd-10,
HEAD
Changes since 1.1: +9 -10
lines
Diff to previous 1.1 (colored)
Introduce membar_acquire/release. Deprecate membar_enter/exit. The names membar_enter/exit were unclear, and the documentation of membar_enter has disagreed with the implementations on sparc, powerpc, and even x86(!) for the entire time it has been in NetBSD. The terms `acquire' and `release' are ubiquitous in the literature today, and have been adopted in the C and C++ standards to mean load-before-load/store and load/store-before-store, respectively, which are exactly the orderings required by acquiring and releasing a mutex, as well as other useful applications like decrementing a reference count and then freeing the underlying object if it went to zero. Originally I proposed changing one word in the documentation for membar_enter to make it load-before-load/store instead of store-before-load/store, i.e., to make it an acquire barrier. I proposed this on the grounds that (a) all implementations guarantee load-before-load/store, (b) some implementations fail to guarantee store-before-load/store, and (c) all uses in-tree assume load-before-load/store. I verified parts (a) and (b) (except, for (a), powerpc didn't even guarantee load-before-load/store -- isync isn't necessarily enough; need lwsync in general -- but it _almost_ did, and it certainly didn't guarantee store-before-load/store). Part (c) might not be correct, however: under the mistaken assumption that atomic-r/m/w then membar-w/rw is equivalent to atomic-r/m/w then membar-r/rw, I only audited the cases of membar_enter that _aren't_ immediately after an atomic-r/m/w. All of those cases assume load-before-load/store. But my assumption was wrong -- there are cases of atomic-r/m/w then membar-w/rw that would be broken by changing to atomic-r/m/w then membar-r/rw: https://mail-index.netbsd.org/tech-kern/2022/03/29/msg028044.html Furthermore, the name membar_enter has been adopted in other places like OpenBSD where it actually does follow the documentation and guarantee store-before-load/store, even if that order is not useful. So the name membar_enter currently lives in a bad place where it means either of two things -- r/rw or w/rw. With this change, we deprecate membar_enter/exit, introduce membar_acquire/release as better names for the useful pair (r/rw and rw/w), and make sure the implementation of membar_enter guarantees both what was documented _and_ what was implemented, making it an alias for membar_sync. While here, rework all of the membar_* definitions and aliases. The new logic follows a rule to make it easier to audit: membar_X is defined as an alias for membar_Y iff membar_X is guaranteed by membar_Y. The `no stronger than' relation is (the transitive closure of): - membar_consumer (r/r) is guaranteed by membar_acquire (r/rw) - membar_producer (w/w) is guaranteed by membar_release (rw/w) - membar_acquire (r/rw) is guaranteed by membar_sync (rw/rw) - membar_release (rw/w) is guaranteed by membar_sync (rw/rw) And, for the deprecated membars: - membar_enter (whether r/rw, w/rw, or rw/rw) is guaranteed by membar_sync (rw/rw) - membar_exit (rw/w) is guaranteed by membar_release (rw/w) (membar_exit is identical to membar_release, but the name is deprecated.) Finally, while here, annotate some of the instructions with their semantics. For powerpc, leave an essay with citations on the unfortunate but -- as far as I can tell -- necessary decision to use lwsync, not isync, for membar_acquire and membar_consumer. Also add membar(3) and atomic(3) man page links.
Revision 1.1.16.2 / (download) - annotate - [select for diffs], Tue Apr 21 19:37:44 2020 UTC (2 years, 9 months ago) by martin
Branch: phil-wifi
Changes since 1.1.16.1: +0 -0
lines
Diff to previous 1.1.16.1 (colored) to branchpoint 1.1 (colored) next main 1.2 (colored)
Ooops, restore accidently removed files from merge mishap
Revision 1.1.16.1, Tue Apr 21 18:41:19 2020 UTC (2 years, 9 months ago) by martin
Branch: phil-wifi
Changes since 1.1: +1 -1
lines
FILE REMOVED
Sync with HEAD
Revision 1.1 / (download) - annotate - [select for diffs], Wed Sep 3 19:34:25 2014 UTC (8 years, 5 months ago) by matt
Branch: MAIN
CVS Tags: tls-maxphys-20171202,
prg-localcount2-base3,
prg-localcount2-base2,
prg-localcount2-base1,
prg-localcount2-base,
prg-localcount2,
phil-wifi-base,
phil-wifi-20200421,
phil-wifi-20200411,
phil-wifi-20200406,
phil-wifi-20191119,
phil-wifi-20190609,
pgoyette-localcount-base,
pgoyette-localcount-20170426,
pgoyette-localcount-20170320,
pgoyette-localcount-20170107,
pgoyette-localcount-20161104,
pgoyette-localcount-20160806,
pgoyette-localcount-20160726,
pgoyette-localcount,
pgoyette-compat-merge-20190127,
pgoyette-compat-base,
pgoyette-compat-20190127,
pgoyette-compat-20190118,
pgoyette-compat-1226,
pgoyette-compat-1126,
pgoyette-compat-1020,
pgoyette-compat-0930,
pgoyette-compat-0906,
pgoyette-compat-0728,
pgoyette-compat-0625,
pgoyette-compat-0521,
pgoyette-compat-0502,
pgoyette-compat-0422,
pgoyette-compat-0415,
pgoyette-compat-0407,
pgoyette-compat-0330,
pgoyette-compat-0322,
pgoyette-compat-0315,
pgoyette-compat,
perseant-stdc-iso10646-base,
perseant-stdc-iso10646,
netbsd-9-base,
netbsd-9-3-RELEASE,
netbsd-9-2-RELEASE,
netbsd-9-1-RELEASE,
netbsd-9-0-RELEASE,
netbsd-9-0-RC2,
netbsd-9-0-RC1,
netbsd-9,
netbsd-8-base,
netbsd-8-2-RELEASE,
netbsd-8-1-RELEASE,
netbsd-8-1-RC1,
netbsd-8-0-RELEASE,
netbsd-8-0-RC2,
netbsd-8-0-RC1,
netbsd-8,
matt-nb8-mediatek-base,
matt-nb8-mediatek,
localcount-20160914,
is-mlppp-base,
is-mlppp,
cjep_sun2x-base1,
cjep_sun2x-base,
cjep_sun2x,
cjep_staticlib_x-base1,
cjep_staticlib_x-base,
cjep_staticlib_x,
bouyer-xenpvh-base2,
bouyer-xenpvh-base1,
bouyer-xenpvh-base,
bouyer-xenpvh,
bouyer-socketcan-base1,
bouyer-socketcan-base,
bouyer-socketcan,
ad-namecache-base3,
ad-namecache-base,
ad-namecache
Branch point for: phil-wifi
New files for OR1K support