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[109.80.100.85]) by smtp.gmail.com with ESMTPSA id h34-v6sm4258920eda.58.2018.08.31.02.43.47 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 31 Aug 2018 02:43:47 -0700 (PDT) Date: Fri, 31 Aug 2018 11:43:42 +0200 From: Andrea Parri To: "Paul E. McKenney" Cc: Andrea Parri , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org, stern@rowland.harvard.edu, will.deacon@arm.com, peterz@infradead.org, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com Subject: Re: [PATCH RFC LKMM 3/7] EXP tools/memory-model: Add more LKMM limitations Message-ID: <20180831094341.GA4634@andrea> References: <20180829211018.GA19646@linux.vnet.ibm.com> <20180829211053.20531-3-paulmck@linux.vnet.ibm.com> <20180830091713.GA4617@andrea> <20180830221814.GQ4225@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180830221814.GQ4225@linux.vnet.ibm.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > > + b. The "unless" RMW operations are not currently modeled: > > > + atomic_long_add_unless(), atomic_add_unless(), > > > + atomic_inc_unless_negative(), and > > > + atomic_dec_unless_positive(). These can be emulated > > > + in litmus tests, for example, by using atomic_cmpxchg(). > > > > There is a prototype atomic_add_unless(): with current herd7, > > > > $ cat atomic_add_unless.litmus > > C atomic_add_unless > > > > {} > > > > P0(atomic_t *u, atomic_t *v) > > { > > int r0; > > int r1; > > > > r0 = atomic_add_unless(u, 1, 2); > > r1 = atomic_read(v); > > } > > > > P1(atomic_t *u, atomic_t *v) > > { > > int r0; > > int r1; > > > > r0 = atomic_add_unless(v, 1, 2); > > r1 = atomic_read(u); > > } > > > > exists (0:r1=0 /\ 1:r1=0) > > > > $ herd7 -conf linux-kernel.cfg atomic_add_unless.litmus > > Test atomic_add_unless Allowed > > States 3 > > 0:r1=0; 1:r1=1; > > 0:r1=1; 1:r1=0; > > 0:r1=1; 1:r1=1; > > No > > Witnesses > > Positive: 0 Negative: 3 > > Condition exists (0:r1=0 /\ 1:r1=0) > > Observation atomic_add_unless Never 0 3 > > Time atomic_add_unless 0.00 > > Hash=fa37a2359831690299e4cc394e45d966 > > > > The last commit in the herdtools7 repo. related to this implementation > > (AFAICT) is: > > > > 9523c340917b6a ("herd/linux: make atomic_add_unless a primitive, so as to yield more precise dependencies for the returned boolean.") > > > > but I can only vaguely remember those dependencies issues now :/ ...; > > maybe we can now solve these issues? or should we change herd7 to re- > > turn a warning? (Notice that this primitive is currently not exported > > to the linux-kernel.def file.) > > Cool! It would be good to add this to the .def file once the underlying > herd7 machinery is ready. And then I would update the documentation > accordingly. Or happily accept a patch updating the documentation, > as the case might be. ;-) Fair enough, ;-) Please feel free to add: Reviewed-by: Andrea Parri Andrea