On Tue, 4 Jul 2023 at 14:24, Matthew Booth <mbooth@xxxxxxxxxx> wrote:
> On Tue, 4 Jul 2023 at 10:45, Yin, Congmin <congmin.yin@xxxxxxxxx> 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
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