On Tue, Feb 17, 2015 at 08:05:32AM -0800, Paul E. McKenney wrote: > > FWIW, we should probably update that table to include control > > dependencies too; we didn't (formally) have those back then I think. > > > > The blob under SMP BARRIER PAIRING does not mention pairing with control > > dependencies; and I'm rather sure I've done so. > > Yep, they should pair as well, though the pairing is limited. > No transitivity, of course. > > So the straightforward approach requires eighteen bits per cell, though > some of them are a bit, ummm, "unusual".
Right, I think the idea was to not mark with 'X' when very unusual, otherwise you do indeed obtain the below 'trivial' matrix. > Sixteen of these are given by > Scenarios 0-15 in http://lwn.net/Articles/573436/, with the barrier on > the side corresponding to the first column and the barrier on the top > corresponding to the second column. The seventeenth bit says whether > you get transitivity chaining after the top access, assuming that it > happens later. The eighteenth bit says whether you get transitivity > chaining before the side access, assuming that it happens earlier. > > The following is a rough first guess, filling in only the diagonal. > Some of the entries are no doubt wrong, and getting them right requires > something like 7*7*18 test cases, which will take some time. So, is > something like this really helpful? > | mb | wmb | rmb | rbd | acq | rel | ctl | > -----+-------+-------+-------+-------+-------+-------+-------+ > mb | 3ffff | X | X | X | X | X | X + > -----+-------+-------+-------+-------+-------+-------+-------+ > wmb | X | 01000 | X | X | X | X | X + > -----+-------+-------+-------+-------+-------+-------+-------+ > rmb | X | X | 00000 | X | X | X | X + > -----+-------+-------+-------+-------+-------+-------+-------+ > rbd | X | X | X | 00000 | X | X | X + > -----+-------+-------+-------+-------+-------+-------+-------+ > acq | X | X | X | X | 00020 | X | X + > -----+-------+-------+-------+-------+-------+-------+-------+ > rel | X | X | X | X | X | 0cc00 | X + > -----+-------+-------+-------+-------+-------+-------+-------+ > ctl | X | X | X | X | X | X | 00020 + > -----+-------+-------+-------+-------+-------+-------+-------+ So maybe make two tables; one with 'obvious' pairings, which would include things like mb - {mb,rmb,wmb}; rmb-wmb; acq-rel; ctl-mb; etc. That table is for people to quickly check 'easy'; like yes wmb-rbd makes sense and rmb-rbd doesn't appear to make sense, I need more reading up. After that do the 'funny' table, which will explain further possible pairings in more detail, like the rmb-rbd pairing. I'm not entirely sure we want to do the 7*7*18 state table, that's a lot of work to exhaustively generate. We should be lazy and demand fill when people come to us. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
