On Thu, Feb 04 2016 at 9:32am -0500, Hannes Reinecke <hare@xxxxxxx> wrote: > On 02/04/2016 03:09 PM, Mike Snitzer wrote: > > On Thu, Feb 04 2016 at 8:58am -0500, > > Hannes Reinecke <hare@xxxxxxx> wrote: > > > >> On 02/04/2016 02:54 PM, Mike Snitzer wrote: > >>> On Thu, Feb 04 2016 at 1:54am -0500, > >>> Hannes Reinecke <hare@xxxxxxx> wrote: > >>> > >> [ .. ] > >>>> But anyway, I'll be looking at your patches. > >>> > >>> Thanks, sadly none of the patches are going to fix the performance > >>> problems but I do think they are a step forward. > >>> > >> Hmm. I've got a slew of patches converting dm-mpath to use atomic_t > >> and bitops; with that we should be able to move to rcu for path > >> lookup and do away with most of the locking. > >> Quite raw, though; drop me a mail if you're interested. > > > > Hmm, ok I just switched m->lock from spinlock_t to rwlock_t, see: > > https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-4.6&id=a5226e23a6958ac9b7ade13a983604c43d232c7d > > > > So any patch you'd have in this area would need rebasing. I'll gladly > > look at what you have (even if it isn't rebased). So yes please share. > > > > (it could be that there isn't a big enough win associated with switching > > to rwlock_t -- that we could get away without doing that particular > > churn.. open to that if you think rwlock_t pointless given we'll take > > the write lock after repeat_count drops to 0) > > > personally, I don't think the switching to a rwlock_t will buy us > anything; for a decent performance you have to set rq_min_io to 1 > anyway, thereby defeating the purpose of the rwlock. OK, I'll drop the rwlock_t commit. > My thinking was rather a different direction: > Move the crucial bits of the multipath structure to atomics, and > split off the path selection code into one bit for selecting the > path within a path group, and another which switches the path groups. > When we do that we could use rcus for the paths themselves, and > would only need to take the spinlock if we need to switch path > groups. Which should be okay as switching path groups is > (potentially) a rather slow operation anyway. If you were to put focus to dusting your work off and helping me get switched over to RCU I'd be very thankful. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
