Somnath,
I wonder if there's a bottleneck or a point of contention for the
kernel. For a entirely uncached workload I expect the page cache
lookup to cause a slow down (since the lookup should be wasted). What
I wouldn't expect is a 45% performance drop. Memory speed should be
one magnitude faster
random
workload..
Thanks & Regards
Somnath
-Original Message-
From: Milosz Tanski [mailto:mil...@adfin.com]
Sent: Tuesday, September 23, 2014 12:09 PM
To: Somnath Roy
Cc: ceph-devel@vger.kernel.org
Subject: Re: Impact of page cache on OSD read performance for SSD
Somnath,
I
t to...
sage
>
> Thanks & Regards
> Somnath
>
> -Original Message-
> From: Milosz Tanski [mailto:mil...@adfin.com]
> Sent: Tuesday, September 23, 2014 12:09 PM
> To: Somnath Roy
> Cc: ceph-devel@vger.kernel.org
> Subject: Re: Impact of page cache on OS
to...
>
> sage
>
>
>>
>> Thanks & Regards
>> Somnath
>>
>> -Original Message-
>> From: Milosz Tanski [mailto:mil...@adfin.com]
>> Sent: Tuesday, September 23, 2014 12:09 PM
>> To: Somnath Roy
>> Cc: ceph-devel@vger.ke
Sage Weil
Cc: Somnath Roy; Milosz Tanski; ceph-devel@vger.kernel.org
Subject: Re: Impact of page cache on OSD read performance for SSD
Good point, but do you have considered that the impaction for write ops? And if
skip page cache, FileStore is responsible for data cache?
On Wed, Sep 24, 2014 at
performance as direct_io.
>
> Thanks & Regards
> Somnath
>
> -Original Message-
> From: Haomai Wang [mailto:haomaiw...@gmail.com]
> Sent: Tuesday, September 23, 2014 7:07 PM
> To: Sage Weil
> Cc: Somnath Roy; Milosz Tanski; ceph-devel@vger.kernel.org
> Subj
gt;> following could be problem.
> >>>
> >>> 1. Double copy (disk -> file buffer cache, file buffer cache -> user
> >>> buffer)
> >>>
> >>> 2. As the iostat output shows, it is not reading 4K only, it is
> >>> reading more
ptember 23, 2014 7:07 PM
To: Sage Weil
Cc: Somnath Roy; Milosz Tanski; ceph-devel@vger.kernel.org
Subject: Re: Impact of page cache on OSD read performance for SSD
Good point, but do you have considered that the impaction for write ops? And if
skip page cache, FileStore is responsible for data cach
ve us a clear
>>>> understanding
>>>> what exactly is going on there and it may turn out that tuning kernel
>>>> parameters only we can achieve similar performance as direct_io.
>>>>
>>>> Thanks & Regards
>>>> Somnath
>&
ly we can achieve similar performance as
>> > direct_io.
>> >
>> > Thanks & Regards
>> > Somnath
>> >
>> > -Original Message-
>> > From: Haomai Wang [mailto:haomaiw...@gmail.com]
>> > Sent: Tuesday, September 23,
o:haomaiw...@gmail.com]
Sent: Wednesday, September 24, 2014 9:06 AM
To: Sage Weil
Cc: Somnath Roy; Milosz Tanski; ceph-devel@vger.kernel.org
Subject: Re: Impact of page cache on OSD read performance for SSD
On Wed, Sep 24, 2014 at 8:38 PM, Sage Weil wrote:
> On Wed, 24 Sep 2014, Haomai Wang wrote
> Cc: Somnath Roy; Milosz Tanski; ceph-devel@vger.kernel.org
> Subject: Re: Impact of page cache on OSD read performance for SSD
>
> On Wed, Sep 24, 2014 at 8:38 PM, Sage Weil wrote:
>> On Wed, 24 Sep 2014, Haomai Wang wrote:
>>> I agree with that direct read will help for
nath Roy
Cc: Sage Weil; Milosz Tanski; ceph-devel@vger.kernel.org
Subject: Re: Impact of page cache on OSD read performance for SSD
On Thu, Sep 25, 2014 at 7:49 AM, Somnath Roy wrote:
> Hi,
> After going through the blktrace, I think I have figured out what is
> going on there. I think kern
...@vger.kernel.org
[mailto:ceph-devel-ow...@vger.kernel.org] On Behalf Of Somnath Roy
Sent: Thursday, September 25, 2014 11:15 AM
To: Haomai Wang
Cc: Sage Weil; Milosz Tanski; ceph-devel@vger.kernel.org
Subject: RE: Impact of page cache on OSD read performance for SSD
It will be definitely hampered
Chen, Xiaoxi [mailto:xiaoxi.c...@intel.com]
Sent: Wednesday, September 24, 2014 10:00 PM
To: Somnath Roy; Haomai Wang
Cc: Sage Weil; Milosz Tanski; ceph-devel@vger.kernel.org
Subject: RE: Impact of page cache on OSD read performance for SSD
Have you ever seen large readahead_kb would hear ra
> Cc: Sage Weil; Milosz Tanski; ceph-devel@vger.kernel.org
> Subject: Re: Impact of page cache on OSD read performance for SSD
>
> On Thu, Sep 25, 2014 at 7:49 AM, Somnath Roy wrote:
> > Hi,
> > After going through the blktrace, I think I have figured out what is
> > g
swers/suggestions.
Thanks & Regards
Somnath
-Original Message-
From: Somnath Roy
Sent: Thursday, September 25, 2014 12:11 AM
To: 'Chen, Xiaoxi'; Haomai Wang
Cc: Sage Weil; Milosz Tanski; ceph-devel@vger.kernel.org
Subject: RE: Impact of page cache on OSD read performance for S
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