On Wed, May 24, 2017 at 05:59:41PM +0900, Byungchul Park wrote: > We can skip adding a dependency 'AX -> B', in case that we ensure 'AX -> > the previous of B in hlocks' to be created, where AX is a crosslock and > B is a typical lock. Remember that two adjacent locks in hlocks generate > a dependency like 'prev -> next', that is, 'the previous of B in hlocks > -> B' in this case. > > For example: > > in hlocks[] > ------------ > ^ A (gen_id: 4) --+ > | | previous gen_id > | B (gen_id: 3) <-+ > | C (gen_id: 3) > | D (gen_id: 2) > oldest | E (gen_id: 1) > > in xhlocks[] > ------------ > ^ A (gen_id: 4, prev_gen_id: 3(B's gen id)) > | B (gen_id: 3, prev_gen_id: 3(C's gen id)) > | C (gen_id: 3, prev_gen_id: 2(D's gen id)) > | D (gen_id: 2, prev_gen_id: 1(E's gen id)) > oldest | E (gen_id: 1, prev_gen_id: NA) > > On commit for a crosslock AX(gen_id = 3), it's engough to add 'AX -> C', > but adding 'AX -> B' and 'AX -> A' is unnecessary since 'AX -> C', 'C -> > B' and 'B -> A' cover them, which are guaranteed to be generated. > > This patch intoduces a variable, prev_gen_id, to avoid adding this kind > of redundant dependencies. In other words, the previous in hlocks will > anyway handle it if the previous's gen_id >= the crosslock's gen_id. >
Didn't we talk about an alternative to this? /me goes dig https://lkml.kernel.org/r/[email protected] There and replies. So how much does this save vs avoiding redundant links?
