On Wed, May 16, 2018 at 8:27 PM, Donald "Mac" McCarthy
<mac@xxxxxxxxxxxxxxx> wrote:
> CephFS. 8 core atom C2758, 16 GB ram, 256GB ssd, 2.5 GB NIC (supermicro microblade node).
>
> Read test:
> dd if=/ceph/1GB.test of=/dev/null bs=1M
Yup, looks like a kcephfs regression. The performance of the above
command is highly dependent on readahead settings and it looks like
that got goofed up.
After mounting w/o options on 7.4:
$ cat /sys/devices/virtual/bdi/ceph-1/read_ahead_kb
8192
Same on 7.5:
$ cat /sys/devices/virtual/bdi/ceph-1/read_ahead_kb
0
As a workaround, try resetting it back to 8192:
# echo 8192 >/sys/devices/virtual/bdi/ceph-1/read_ahead_kb
Thanks,
Ilya
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