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Date:	Tue, 20 May 2014 13:59:05 +0000
From:	Felipe Franciosi <felipe.franciosi@...rix.com>
To:	'Vitaly Kuznetsov' <vkuznets@...hat.com>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"axboe@...nel.dk" <axboe@...nel.dk>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	"jerry.snitselaar@...cle.com" <jerry.snitselaar@...cle.com>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	"Roger Pau Monne" <roger.pau@...rix.com>
Subject: RE: [Xen-devel] Backport request to stable of two performance
 related fixes for xen-blkfront (3.13 fixes to earlier trees)

I had a small side-bar thread with Vitaly discussing the comprehensiveness of his measurements and how his tests are being conducted. He will report new results as they become available.

In the meantime, I stand behind that the patches need to be backported and there is a regression if we don't do that.
Ubuntu has already provided a test kernel with the patches pulled in.  I will test those as soon as I get the chance (hopefully by the end of the week).
See: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1319003

Felipe

> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> Sent: 20 May 2014 12:41
> To: Roger Pau Monne
> Cc: Konrad Rzeszutek Wilk; axboe@...nel.dk; Felipe Franciosi;
> gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org;
> stable@...r.kernel.org; jerry.snitselaar@...cle.com; xen-
> devel@...ts.xenproject.org
> Subject: Re: [Xen-devel] Backport request to stable of two performance
> related fixes for xen-blkfront (3.13 fixes to earlier trees)
> 
> Roger Pau Monné <roger.pau@...rix.com> writes:
> 
> > On 20/05/14 11:54, Vitaly Kuznetsov wrote:
> >> Vitaly Kuznetsov <vkuznets@...hat.com> writes:
> >>
> >>> 1) ramdisks (/dev/ram*) (persistent grants and indirect descriptors
> >>> disabled)
> >>
> >> sorry, there was a typo. persistent grants and indirect descriptors
> >> are enabled with ramdisks, otherwise such testing won't make any sense.
> >
> > I'm not sure how is that possible, from your description I get that
> > you are using 3.11 on the Dom0, which means blkback has support for
> > persistent grants and indirect descriptors, but the guest is RHEL7,
> > that's using the 3.10 kernel AFAICT, and this kernel only has
> > persistent grants implemented.
> 
> RHEL7 kernel is mostly merged with 3.11 in its Xen part, we have indirect
> descriptors backported.
> 
> Actually I tried my tests with upstream (Fedora) kernel and results were
> similar. I can try comparing e.g. 3.11.10 with 3.12.0 and provide exact
> measurements.
> 
> --
>   Vitaly

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