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

[Chris Mason <clm@fb.com>]

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

> And that is the larger problem, what can we do about that issue.
> Honestly, I don't think much, as it takes money from companies to commit
> to do this work, which no one seems to ever want to do.  What make this
> year the year that something different happens?

I can't promise different.  At best we'll tease out some new benchmarks
and try to get them into a format that get run often.

-chris