linux-kernel - Re: Backport request to stable of two performance related fixes for xen-blkfront (3.13 fixes to earlier trees)

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Date:	Fri, 06 Jun 2014 12:58:20 +0200
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	xen-devel@...ts.xenproject.org, felipe.franciosi@...rix.com,
	roger.pau@...rix.com, jerry.snitselaar@...cle.com, axboe@...nel.dk
Subject: Re: Backport request to stable of two performance related fixes for xen-blkfront (3.13 fixes to earlier trees)

Jiri Slaby <jslaby@...e.cz> writes:

> On 06/04/2014 07:48 AM, Greg KH wrote:
>> On Wed, May 14, 2014 at 03:11:22PM -0400, Konrad Rzeszutek Wilk wrote:
>>> Hey Greg
>>>
>>> This email is in regards to backporting two patches to stable that
>>> fall under the 'performance' rule:
>>>
>>>  bfe11d6de1c416cea4f3f0f35f864162063ce3fa
>>>  fbe363c476afe8ec992d3baf682670a4bd1b6ce6
>> 
>> Now queued up, thanks.
>
> AFAIU, they introduce a performance regression.
>
> Vitaly?

I'm aware of a performance regression in a 'very special' case when
ramdisks or files on tmpfs are being used as storage, I post my results
a while ago:
https://lkml.org/lkml/2014/5/22/164
I'm not sure if that 'special' case requires investigation and/or should
prevent us from doing stable backport but it would be nice if someone
tries to reproduce it at least.

I'm going to make a bunch of tests with FusionIO drives and sequential
read to replicate same test Felipe did, I'll report as soon as I have
data (beginning of next week hopefuly).

-- 
  Vitaly
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