On Wed, Nov 07 2018 at 5:29pm -0500, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > On Tue, Nov 06 2018 at 4:34pm -0500, > Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > Hi > > > > These are the device mapper percpu patches. > > > > Note that I didn't test request-based device mapper because I don't have > > hardware for it (the patches don't convert request-base targets to percpu > > values, but there are a few inevitable changes in dm-rq.c). > > Patches 1 - 3 make sense. But the use of percpu inflight counters isn't > something I can get upstream. Any more scalable counter still needs to > be wired up to the block stats interfaces (the one you did in patch 5 is > only for the "inflight" fsffs file, there is also the generic diskstats > callout to part_in_flight(), etc). Wiring up both part_in_flight() and > part_in_flight_rw() to optionally callout to a new callback isn't going > to fly.. especially if that callout is looping up the sum of percpu > counters. > > I checked with Jens and now that in 4.21 all of the old request-based IO > path is gone (and given that blk-mq bypasses use of ->in_flight[]): the > only consumer of the existing ->in_flight[] is the bio-based IO path. > > Given that now only bio-based is consuming it, and your work was focused > on making bio-based DM's "pending" IO accounting more scalable, it is > best to just change block core's ->in_flight[] directly. > > But Jens is against switching to using percpu counters because they are > really slow when summing the counts. And diskstats does that > frequently. Jens said at least 2 other attempts were made and rejected > to switch over to percpu counters. > > Jens' suggestion is to implement a new generic rolling per-node > counter. Would you be open to trying that? I've based my dm-4.21 branch on Jens' for-4.21/block branch and staged your first 3 patches. If you're interested in exploring rolling per-node inflight counters please base your work on this branch: https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/log/?h=dm-4.21 ("rolling per-node counters" aside, any new DM development should be based on the dm-4.21 branch) Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
