Re: [Ksummit-discuss] [TOPIC] Application performance: regressions, controlling preemption

[Li Zefan <lizefan@huawei.com>]

On 2014/5/13 9:43, Chris Mason wrote:
> On 05/12/2014 07:16 PM, Greg KH wrote:
>> On Mon, May 12, 2014 at 10:32:27AM -0400, Chris Mason wrote:
>>> Hi everyone,
>>>
>>> We're in the middle of upgrading the tiers here from older kernels 
>>> (2.6.38, 3.2) into 3.10 and higher.
>>>
>>> I've been doing this upgrade game for a number of years now, with 
>>> different business cards taped to my forehead and with different target 
>>> workloads.
>>>
>>> The result is always the same...if I'm really lucky the system isn't 
>>> slower, but usually I'm left with a steaming pile of 10-30% regressions.
>>
>> How long have we been having this discussion?  8 years?  It's not like
>> people don't know that performance testing needs to be constantly
>> happening, we've been saying that for a long time.  It's just that no
>> one seems to listen to us :(
>>
> 
> Yes and no.  Intel listened, and I think they have had a huge positive
> impact here.  Others have as well, maybe not as consistently, but still.
> 
> I do find it really interesting that even with huge improvements all
> over the place, we have a very hard time upgrading production workloads
> without hitting big regressions.
> 
> Sometimes it is just a few .config entries,

Do you mean some regressions are introduced by new configs i.e. new
features? If so, I don't think that can be strictly called regressions.

> and sometimes we paper over
> it with improvements in other areas, but it's almost always worse.
>