linux-kernel - Re: [PATCH] arm: armv7: perf: fix armv7 ref-cycles error

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Date:	Thu, 9 Oct 2014 06:51:30 -0700
From:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:	zhangzhiqiang <zhangzhiqiang.zhang@...wei.com>
Cc:	Will Deacon <will.deacon@....com>,
	Mark Rutland <Mark.Rutland@....com>,
	"cov@...eaurora.org" <cov@...eaurora.org>,
	"lizefan@...wei.com" <lizefan@...wei.com>,
	"wangnan0@...wei.com" <wangnan0@...wei.com>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm: armv7: perf: fix armv7 ref-cycles error

On Thu, Oct 09, 2014 at 03:13:00PM +0800, zhangzhiqiang wrote:
> On 2014/10/9 11:41, gregkh@...uxfoundation.org wrote:
> > On Thu, Oct 09, 2014 at 11:07:04AM +0800, zhangzhiqiang wrote:
> >> On 2014/10/8 21:38, Will Deacon wrote:
> >>> On Wed, Oct 08, 2014 at 02:31:47PM +0100, gregkh@...uxfoundation.org wrote:
> >>>> On Wed, Oct 08, 2014 at 10:17:41AM +0100, Will Deacon wrote:
> >>>>> On Wed, Oct 08, 2014 at 04:06:12AM +0100, zhangzhiqiang wrote:
> >>>>>> hi all,
> >>>>>> ----------------------------------------
> >>>>>>
> >>>>>> ref-cycles event is specially to Intel core, but can still used in arm architecture
> >>>>>> with the wrong return value with 3.10 stable. for instance:
> >>>>>>
> >>>>>>  perf stat -e ref-cycles sleep 1
> >>>>>>
> >>>>>>  Performance counter stats for 'sleep 1':
> >>>>>>
> >>>>>>   	0 ref-cycles
> >>>>>>
> >>>>>>        1.002381916 seconds time elapsed
> >>>>>>
> >>>>>> this patch fix the bug and make it return NOT SUPPORTED
> >>>>>> distinctly.
> >>>>>>
> >>>>>> In upstream this bug has been fixed by other way(not primary for the bug), which changes more than one file
> >>>>>> and more than 1000 lines. the primary commit is 6b7658ec8a100b608e59e3cde353434db51f5be0.
> >>>>>> besides we can not simply cherry-pick.
> >>>>>
> >>>>> I thought I saw Greg pick this up the other day?
> >>>>
> >>>> Yes, it's in 3.16.4, did I do something wrong by accepting it?
> >>>
> >>> Nah, it's a trivial patch that I struggle to get excited about. I'm just not
> >>> sure why it's being sent again, after you already accepted it.
> >>
> >> Yes, it's in 3.16.4, in my opinion 3.10 need it too, can we put it into 3.10 or
> >> do we have the plan?
> > 
> > Does it apply to 3.10-stable?  Did you test it there and see if it
> > resolves your issue?
> 
> I have tested in 3.10.56, the bug is still existing and the patch is apply to 3.10-stable.
> Follow is the result without/with this patch based on 3.10.56.
> 
> 3.10.56 without the patch:
> bash-4.2# perf stat -e ref-cycles sleep 1
> 
>  Performance counter stats for 'sleep 1':
> 
>                  0 ref-cycles
> 
>        1.002461500 seconds time elapsed
> 
> 3.10.56 with the patch:
> bash-4.2# perf stat -e ref-cycles sleep 1
> 
>  Performance counter stats for 'sleep 1':
> 
>    <not supported> ref-cycles
> 
>        1.002385243 seconds time elapsed

Given I have no idea what the patch even does, or is supposed to be
doing, I don't know how to answer this, except it looks like I shouldn't
be applying this to the 3.10-stable kernel series :)

sorry,

greg k-h
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