Yes Haomai... -----Original Message----- From: Haomai Wang [mailto:haomaiwang@xxxxxxxxx] Sent: Wednesday, September 17, 2014 7:28 PM To: Somnath Roy Cc: Sage Weil; Josh Durgin; ceph-devel@xxxxxxxxxxxxxxx Subject: Re: severe librbd performance degradation in Giant According http://tracker.ceph.com/issues/9513, do you mean that rbd cache will make 10x performance degradation for random read? On Thu, Sep 18, 2014 at 7:44 AM, Somnath Roy <Somnath.Roy@xxxxxxxxxxx> wrote: > Josh/Sage, > I should mention that even after turning off rbd cache I am getting ~20% degradation over Firefly. > > Thanks & Regards > Somnath > > -----Original Message----- > From: Somnath Roy > Sent: Wednesday, September 17, 2014 2:44 PM > To: Sage Weil > Cc: Josh Durgin; ceph-devel@xxxxxxxxxxxxxxx > Subject: RE: severe librbd performance degradation in Giant > > Created a tracker for this. > > http://tracker.ceph.com/issues/9513 > > Thanks & Regards > Somnath > > -----Original Message----- > From: ceph-devel-owner@xxxxxxxxxxxxxxx > [mailto:ceph-devel-owner@xxxxxxxxxxxxxxx] On Behalf Of Somnath Roy > Sent: Wednesday, September 17, 2014 2:39 PM > To: Sage Weil > Cc: Josh Durgin; ceph-devel@xxxxxxxxxxxxxxx > Subject: RE: severe librbd performance degradation in Giant > > Sage, > It's a 4K random read. > > Thanks & Regards > Somnath > > -----Original Message----- > From: Sage Weil [mailto:sweil@xxxxxxxxxx] > Sent: Wednesday, September 17, 2014 2:36 PM > To: Somnath Roy > Cc: Josh Durgin; ceph-devel@xxxxxxxxxxxxxxx > Subject: RE: severe librbd performance degradation in Giant > > What was the io pattern? Sequential or random? For random a slowdown makes sense (tho maybe not 10x!) but not for sequentail.... > > s > > On Wed, 17 Sep 2014, 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:josh.durgin@xxxxxxxxxxx] >> Sent: Wednesday, September 17, 2014 2:20 PM >> To: Somnath Roy; ceph-devel@xxxxxxxxxxxxxxx >> 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. 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