Re: [PATCH 3/3] xen/block: add multi-page ring support

["Roger Pau Monné" <roger.pau@citrix.com>]

El 09/06/15 a les 15.39, Konrad Rzeszutek Wilk ha escrit:
> On Tue, Jun 09, 2015 at 08:52:53AM +0000, Paul Durrant wrote:
>>> -----Original Message-----
>>> From: Bob Liu [mailto:bob.liu@oracle.com]
>>> Sent: 09 June 2015 09:50
>>> To: Bob Liu
>>> Cc: xen-devel@lists.xen.org; David Vrabel; justing@spectralogic.com;
>>> konrad.wilk@oracle.com; Roger Pau Monne; Paul Durrant; Julien Grall; linux-
>>> kernel@vger.kernel.org
>>> Subject: Re: [PATCH 3/3] xen/block: add multi-page ring support
>>>
>>>
>>> On 06/03/2015 01:40 PM, Bob Liu wrote:
>>>> Extend xen/block to support multi-page ring, so that more requests can be
>>>> issued by using more than one pages as the request ring between blkfront
>>>> and backend.
>>>> As a result, the performance can get improved significantly.
>>>>
>>>> We got some impressive improvements on our highend iscsi storage cluster
>>>> backend. If using 64 pages as the ring, the IOPS increased about 15 times
>>>> for the throughput testing and above doubled for the latency testing.
>>>>
>>>> The reason was the limit on outstanding requests is 32 if use only one-page
>>>> ring, but in our case the iscsi lun was spread across about 100 physical
>>>> drives, 32 was really not enough to keep them busy.
>>>>
>>>> Changes in v2:
>>>>  - Rebased to 4.0-rc6.
>>>>  - Document on how multi-page ring feature working to linux io/blkif.h.
>>>>
>>>> Changes in v3:
>>>>  - Remove changes to linux io/blkif.h and follow the protocol defined
>>>>    in io/blkif.h of XEN tree.
>>>>  - Rebased to 4.1-rc3
>>>>
>>>> Changes in v4:
>>>>  - Turn to use 'ring-page-order' and 'max-ring-page-order'.
>>>>  - A few comments from Roger.
>>>>
>>>> Changes in v5:
>>>>  - Clarify with 4k granularity to comment
>>>>  - Address more comments from Roger
>>>>
>>>> Signed-off-by: Bob Liu <bob.liu@oracle.com>
>>>
>>> Also tested the windows PV driver which also works fine when multi-page
>>> ring feature
>>> was enabled in Linux backend.
>>> http://www.xenproject.org/downloads/windows-pv-drivers.html
>>>
>>
>> Great! Thanks for verifying that :-)
> 
> Woot! Bob, could you repost the blkif.h patch for the Xen tree
> pleas e and also mention the testing part in it please? I think this
> was the only big 'what if?!' question holding this up.
> 
> 
> Roger, I put them (patches) on devel/for-jens-4.2 on
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git
> 
> I think these two patches:
> drivers: xen-blkback: delay pending_req allocation to connect_ring
> xen/block: add multi-page ring support
> 
> are the only ones that haven't been Acked by you (or maybe they
> have and I missed the Ack?)

Hello,

I was waiting to Ack those because the XenServer storage performance
folks found out that these patches cause a performance regression on
some of their tests. I'm adding them to the conversation so they can
provide more details about the issues they found, and whether we should
hold pushing this patches or not.

Roger.