On Mon, Oct 23, 2017 at 2:16 AM, Peter Desnoyers <pjd@xxxxxxxxxxx> wrote: > We’re emulating some in-disk algorithms in a device mapper target, and would like to be able to do a fair comparison between the emulated and real versions; however they see radically different I/O streams, evidently because there’s no scheduling / request merging / etc. on top of the bio-based device mapper target. > > It appears that if our device mapper were request-based instead of bio-based we wouldn’t have this issue, but after reading a bunch of history on the mailing list archives I don’t think this is going to happen easily. > > Does anyone have any thoughts on quick-and-dirty ways to approximate this so we can get some preliminary measurements? dm-multipath won’t stack on a bio-based target, and attempts to stack loopback and various iscsi targets on top haven’t achieved the desired results. (in general these have resulted in our dm target seeing individual 4K I/Os, instead of the larger I/Os at the higher layer) > I posted out one patchset for addressing the issue: https://marc.info/?l=linux-block&m=150677334021817&w=2 But it has been obsolete, will post out a new version when I get time to do that. -- Ming Lei -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
