Re: severe librbd performance degradation in Giant

[Mark Nelson <mark.nelson@inktank.com>]

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@gmail.com>
> À: "Somnath Roy" <Somnath.Roy@sandisk.com>
> Cc: "Sage Weil" <sweil@redhat.com>, "Josh Durgin" <josh.durgin@inktank.com>, ceph-devel@vger.kernel.org
> 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@sandisk.com> 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@vger.kernel.org
>> 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@vger.kernel.org [mailto:ceph-devel-owner@vger.kernel.org] On Behalf Of Somnath Roy
>> Sent: Wednesday, September 17, 2014 2:39 PM
>> To: Sage Weil
>> Cc: Josh Durgin; ceph-devel@vger.kernel.org
>> 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@redhat.com]
>> Sent: Wednesday, September 17, 2014 2:36 PM
>> To: Somnath Roy
>> Cc: Josh Durgin; ceph-devel@vger.kernel.org
>> 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@inktank.com]
>>> Sent: Wednesday, September 17, 2014 2:20 PM
>>> To: Somnath Roy; ceph-devel@vger.kernel.org
>>> 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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