It's default read ahead setting. I am doing random read , so, I don't think read ahead is the issue. Also, in the cluster side, ceph -s is reporting same iops, so, ios are hitting the cluster. -----Original Message----- From: Mark Nelson [mailto:[email protected]] Sent: Wednesday, September 17, 2014 2:34 PM To: Somnath Roy; Josh Durgin; [email protected] Subject: Re: severe librbd performance degradation in Giant
Any chance read ahead could be causing issues? On 09/17/2014 04:29 PM, Somnath Roy wrote: > I set the following in the client side /etc/ceph/ceph.conf where I am running > fio rbd. > > rbd_cache_writethrough_until_flush = false > > But, no difference. BTW, I am doing Random read, not write. Still this > setting applies ? > > Next, I tried to tweak the rbd_cache setting to false and I *got back* the > old performance. Now, it is similar to firefly throughput ! > > So, loks like rbd_cache=true was the culprit. > > Thanks Josh ! > > Regards > Somnath > > -----Original Message----- > From: Josh Durgin [mailto:[email protected]] > Sent: Wednesday, September 17, 2014 2:20 PM > To: Somnath Roy; [email protected] > Subject: Re: severe librbd performance degradation in Giant > > On 09/17/2014 01:55 PM, Somnath Roy wrote: >> Hi Sage, >> We are experiencing severe librbd performance degradation in Giant over >> firefly release. Here is the experiment we did to isolate it as a librbd >> problem. >> >> 1. Single OSD is running latest Giant and client is running fio rbd on top >> of firefly based librbd/librados. For one client it is giving ~11-12K iops >> (4K RR). >> 2. Single OSD is running Giant and client is running fio rbd on top of Giant >> based librbd/librados. For one client it is giving ~1.9K iops (4K RR). >> 3. Single OSD is running latest Giant and client is running Giant based >> ceph_smaiobench on top of giant librados. For one client it is giving >> ~11-12K iops (4K RR). >> 4. Giant RGW on top of Giant OSD is also scaling. >> >> >> So, it is obvious from the above that recent librbd has issues. I will raise >> a tracker to track this. > > For giant the default cache settings changed to: > > rbd cache = true > rbd cache writethrough until flush = true > > If fio isn't sending flushes as the test is running, the cache will stay in > writethrough mode. Does the difference remain if you set rbd cache > writethrough until flush = false ? > > Josh > > ________________________________ > > PLEASE NOTE: The information contained in this electronic mail message is > intended only for the use of the designated recipient(s) named above. If the > reader of this message is not the intended recipient, you are hereby notified > that you have received this message in error and that any review, > dissemination, distribution, or copying of this message is strictly > prohibited. If you have received this communication in error, please notify > the sender by telephone or e-mail (as shown above) immediately and destroy > any and all copies of this message in your possession (whether hard copies or > electronically stored copies). > > -- > To unsubscribe from this list: send the line "unsubscribe ceph-devel" > in the body of a message to [email protected] More majordomo > info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
