Re: Impact of page cache on OSD read performance for SSD

2014-09-23 Thread Milosz Tanski
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

RE: Impact of page cache on OSD read performance for SSD

2014-09-23 Thread Somnath Roy
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

RE: Impact of page cache on OSD read performance for SSD

2014-09-23 Thread Sage Weil
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

Re: Impact of page cache on OSD read performance for SSD

2014-09-23 Thread Haomai Wang
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

RE: Impact of page cache on OSD read performance for SSD

2014-09-23 Thread Somnath Roy
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

Re: Impact of page cache on OSD read performance for SSD

2014-09-23 Thread Haomai Wang
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

Re: Impact of page cache on OSD read performance for SSD

2014-09-24 Thread Sage Weil
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

Re: Impact of page cache on OSD read performance for SSD

2014-09-24 Thread Mark Nelson
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

Re: Impact of page cache on OSD read performance for SSD

2014-09-24 Thread Milosz Tanski
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 >&

Re: Impact of page cache on OSD read performance for SSD

2014-09-24 Thread Haomai Wang
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,

RE: Impact of page cache on OSD read performance for SSD

2014-09-24 Thread Somnath Roy
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

Re: Impact of page cache on OSD read performance for SSD

2014-09-24 Thread Haomai Wang
> 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

RE: Impact of page cache on OSD read performance for SSD

2014-09-24 Thread Somnath Roy
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

RE: Impact of page cache on OSD read performance for SSD

2014-09-24 Thread Chen, Xiaoxi
...@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

RE: Impact of page cache on OSD read performance for SSD

2014-09-25 Thread Somnath Roy
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

RE: Impact of page cache on OSD read performance for SSD

2014-09-25 Thread Sage Weil
> 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

RE: Impact of page cache on OSD read performance for SSD

2014-09-29 Thread Somnath Roy
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