On 09/18/2014 04:49 AM, Alexandre DERUMIER wrote:
According http://tracker.ceph.com/issues/9513, do you mean that rbd
cache will make 10x performance degradation for random read?
Hi, on my side, I don't see any degradation performance on read (seq or rand) with or without.
firefly : around 12000iops (with or without rbd_cache)
giant : around 12000iops (with or without rbd_cache)
(and I can reach around 20000-30000 iops on giant with disabling optracker).
rbd_cache only improve write performance for me (4k block )
I can't do it right now since I'm in the middle of reinstalling fedora
on the test nodes, but I will try to replicate this as well if we
haven't figured it out before hand.
Mark
----- Mail original -----
De: "Haomai Wang" <haomaiwang@xxxxxxxxx>
À: "Somnath Roy" <Somnath.Roy@xxxxxxxxxxx>
Cc: "Sage Weil" <sweil@xxxxxxxxxx>, "Josh Durgin" <josh.durgin@xxxxxxxxxxx>, ceph-devel@xxxxxxxxxxxxxxx
Envoyé: Jeudi 18 Septembre 2014 04:27:56
Objet: 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
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