On 03/01/2016 10:03 PM, min fang wrote:
thanks, with your help, I set the read ahead parameter. What is the cache parameter for kernel module rbd? Such as: 1) what is the cache size? 2) Does it support write back? 3) Will read ahead be disabled if max bytes has been read into cache? (similar the concept as "rbd_readahead_disable_after_bytes".
The kernel rbd module does not implement any caching itself. If you're doing I/O to a file on a filesystem on top of a kernel rbd device,
it will go through the usual kernel page cache (unless you use O_DIRECT of course). Josh
2016-03-01 21:31 GMT+08:00 Adrien Gillard <gillard.adrien@xxxxxxxxx <mailto:gillard.adrien@xxxxxxxxx>>: As Tom stated, RBD cache only works if your client is using librbd (KVM clients for instance). Using the kernel RBD client, one of the parameter you can tune to optimize sequential read is increasing /sys/class/block/rbd4/queue/read_ahead_kb Adrien On Tue, Mar 1, 2016 at 12:48 PM, min fang <louisfang2013@xxxxxxxxx <mailto:louisfang2013@xxxxxxxxx>> wrote: I can use the following command to change parameter, for example as the following, but not sure whether it will work. ceph --admin-daemon /var/run/ceph/ceph-mon.openpower-0.asok config set rbd_readahead_disable_after_bytes 0 2016-03-01 15:07 GMT+08:00 Tom Christensen <pavera@xxxxxxxxx <mailto:pavera@xxxxxxxxx>>: If you are mapping the RBD with the kernel driver then you're not using librbd so these settings will have no effect I believe. The kernel driver does its own caching but I don't believe there are any settings to change its default behavior. On Mon, Feb 29, 2016 at 9:36 PM, Shinobu Kinjo <skinjo@xxxxxxxxxx <mailto:skinjo@xxxxxxxxxx>> wrote: You may want to set "ioengine=rbd", I guess. Cheers, ----- Original Message ----- From: "min fang" <louisfang2013@xxxxxxxxx <mailto:louisfang2013@xxxxxxxxx>> To: "ceph-users" <ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx>> Sent: Tuesday, March 1, 2016 1:28:54 PM Subject: rbd cache did not help improve performance Hi, I set the following parameters in ceph.conf [client] rbd cache=true rbd cache size= 25769803776 rbd readahead disable after byte=0 map a rbd image to a rbd device then run fio testing on 4k read as the command ./fio -filename=/dev/rbd4 -direct=1 -iodepth 64 -thread -rw=read -ioengine=aio -bs=4K -size=500G -numjobs=32 -runtime=300 -group_reporting -name=mytest2 Compared the result with setting rbd cache=false and enable cache model, I did not see performance improved by librbd cache. Is my setting not right, or it is true that ceph librbd cache will not have benefit on 4k seq read? thanks. _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx <mailto:ceph-users@xxxxxxxxxxxxxx> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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