On Mon, Jul 3, 2023 at 6:58 PM Mark Nelson <mark.nel...@clyso.com> wrote: > > > On 7/3/23 04:53, Matthew Booth wrote: > > On Thu, 29 Jun 2023 at 14:11, Mark Nelson <mark.nel...@clyso.com> wrote: > >>>>> This container runs: > >>>>> fio --rw=write --ioengine=sync --fdatasync=1 > >>>>> --directory=/var/lib/etcd --size=100m --bs=8000 --name=etcd_perf > >>>>> --output-format=json --runtime=60 --time_based=1 > >>>>> > >>>>> And extracts sync.lat_ns.percentile["99.000000"] > >>>> Matthew, do you have the rest of the fio output captured? It would be > >>>> interesting to see if it's just the 99th percentile that is bad or the > >>>> PWL cache is worse in general. > >>> Sure. > >>> > >>> With PWL cache: https://paste.openstack.org/show/820504/ > >>> Without PWL cache: https://paste.openstack.org/show/b35e71zAwtYR2hjmSRtR/ > >>> With PWL cache, 'rbd_cache'=false: > >>> https://paste.openstack.org/show/byp8ZITPzb3r9bb06cPf/ > >> > >> Also, how's the CPU usage client side? I would be very curious to see > >> if unwindpmp shows anything useful (especially lock contention): > >> > >> > >> https://github.com/markhpc/uwpmp > >> > >> > >> Just attach it to the client-side process and start out with something > >> like 100 samples (more are better but take longer). You can run it like: > >> > >> > >> ./unwindpmp -n 100 -p <pid> > > I've included the output in this gist: > > https://gist.github.com/mdbooth/2d68b7e081a37e27b78fe396d771427d > > > > That gist contains 4 runs: 2 with PWL enabled and 2 without, and also > > a markdown file explaining the collection method. > > > > Matt > > > Thanks Matt! I looked through the output. Looks like the symbols might > have gotten mangled. I'm not an expert on the RBD client, but I don't > think we would really be calling into > rbd_group_snap_rollback_with_progress from > librbd::cache::pwl::ssd::WriteLogEntry::writeback_bl. Was it possible > you used the libdw backend for unwindpmp? libdw sometimes gives > strange/mangled callgraphs, but I haven't seen it before with > libunwind. Hopefully Congmin Yin or Ilya can confirm if it's garbage.
> > So with that said, assuming we can trust these callgraphs at all, it > looks like it might be worth looking at the latency of the > AbstractWriteLog, librbd::cache::pwl::ssd::WriteLogEntry::writeback_bl, > and possibly usage of librados::v14_2_0::IoCtx::object_list. On the Hi Mark, Both rbd_group_snap_rollback_with_progress and librados::v14_2_0::IoCtx::object_list entries don't make sense to me, so I'd say it's garbage. Thanks, Ilya _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-le...@ceph.io