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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Jun 09, 2015 at 04:07:33PM +0200, Roger Pau Monné wrote:
> 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@xxxxxxxxxx]
> >>> Sent: 09 June 2015 09:50
> >>> To: Bob Liu
> >>> Cc: xen-devel@xxxxxxxxxxxxx; David Vrabel; justing@xxxxxxxxxxxxxxxx;
> >>> konrad.wilk@xxxxxxxxxx; Roger Pau Monne; Paul Durrant; Julien Grall; 
> >>> linux-
> >>> kernel@xxxxxxxxxxxxxxx
> >>> 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@xxxxxxxxxx>
> >>>
> >>> 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

This is with multi-page enabled or with the patches but multi-page
disabled (baseline)?

> provide more details about the issues they found, and whether we should
> hold pushing this patches or not.

Or surely fix whatever is causing this.
> 
> Roger.
> 

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