On Tue, 4 Jul 2023 at 14:24, Matthew Booth <mbooth@redhat.com> wrote:
On Tue, 4 Jul 2023 at 10:45, Yin, Congmin <congmin.yin@intel.com> wrote:
Hi , Matthew
I see "rbd with pwl cache: 5210112 ns", This latency is beyond my expectations and I believe it is unlikely to occur. In theory, this value should be around a few hundred microseconds. But I'm not sure what went wrong in your steps. Can you use perf for latency analysis. Hi @Ilya Dryomov , do you have any suggestions?
I don't think the absolute value is interesting to you: it's the output of a specific benchmarking test (described in detail below) which likely has multiple additional layers involved. It's also a 99th percentile value so most likely includes jitter from other subsystems, although note that it is very reproducible and the test system has no other load. The interesting thing here is the difference between 'rbd with pwl' and 'pwl cache device'. Why is the latency performance of 'rbd with pwl' so much worse than the device which is holding the pwl cache?
Perf, some command: admin_socket = /mnt/pmem/cache.asok ceph --admin-daemon /mnt/pmem/cache.asok perf reset all ceph --admin-daemon /mnt/pmem/cache.asok perf dump
To give you an idea of my confusion, here's what I'm running on the client, which is not running any ceph daemons: # admin_socket=/var/lib/libvirt/images/pwl/cache.sock # ceph --admin-daemon ${admin_socket} perf reset all admin_socket: exception getting command descriptions: [Errno 2] No such file or directory What should be listening on that socket? Do you have a link to any documentation which would help me get this up and running? Thanks, Matt -- Matthew Booth