Great! this is what I wanted to hear :) Fully agree.
> On Thu, 06 Jul 2006 14:44:23 +0400, Kirill Korotaev wrote:
>>>>>>I assuming you are doing your tests on the same system (i.e. same
>>>>>>compiler/libs/whatever else), and you do not change that system over
>>>>>>time (i.e. you do not upgrade gcc on it in between the tests).
>>>>>I hope! :)
>>>>All binaries should be built statically to work the same way inside host/guest or
>>>>you need to make sure that you have exactly the same versions of glibc and other
>>>>system libraries. At least glibc can affect perforamnce very much :/
>>>Ick - no one builds binaries statically in the real world. And,
>>>when you build binaries statically, you lose all ability to fix
>>>security problems in base libraries by doing an update of that library.
>>>Instead, all applications need to be rebuilt.
>>>Performance tests should reflect real end user usage - not contrived
>>>situations that make a particular solution look better or worse.
>>>If glibc can affect performance, that should be demonstrated in the
>>>real performance results - it is part of the impact of the solution and
>>>may need an additional solution or discussion.
>>What I tried to say is that performance results done in different
>>environments are not comparable so have no much meaning. I don't want us
>>to waste our time digging in why one environment is a bif faster or slower than another.
>>I hope you don't want too.
> I *do* want to understand why one patch set or another is significantly
> faster or slower than any other. I think by now everyone realizes that
> what goes into mainline will not be some slice of vserver, or OpenVZ
> or MetaCluster or Eric's work in progress. It will be the convergance
> of the patches that enable all solutions, and those patches will be added
> as they are validated as beneficial to all participants *and* beneficial
> (or not harmful) to mainline Linux. So, testing of large environments
> is good to see where the overall impacts are (btw, people should start
> reading up on basic oprofile use by about now ;-) but in the end, each
> set of patches for each subsystem will be judged on their own merits.
> Those merits include code cleanliness, code maintainainability, code
> functionality, performance, testability, etc.
> So, you are right that testing which compares roughly similar environments
> is good. But those tests will help us identify areas where one solution
> or another may have code which provides functionality in some way which
> has lower impact.
> I do not want to have to dig into those results in great detail if the
> difference between two approaches is minor. However, if a particular
> area has major impacts to performance, we need to understand how the
> approaches differ and why one solution has greater impact than another.
> Sometimes it is just a coding issue that can be easily addressed. Sometimes
> it will be a design issue indicating that one solution or another has
> a design issue which might have been better addressed by another solution.
> The fun thing here (well, maybe not for each solution provider) is that
> we get to cherry pick the best implementations from each solution, or
> create new ones as we go which ultimate allow us to have application
> virtualization, containers, or whatever you want to call them.
>>Now, to have the same environment there are at least 2 ways:
>>- make static binaries (not that good, but easiest way)
> This is a case where "easiest" is just plain wrong. If it doesn't match
> how people will use their distros and solutions out of the box it has
> no real relevence to the code that will get checked in.
>>- have exactly the same packages in host/VPS for all test cases.
>>BTW, I also prefer 2nd way, but it is harder.
> Herbert's suggestion here is good - if you can use exactly the same
> filesystem for performance comparisons you remove one set of variables.
> However, I also believe that if the difference between any two filesystems
> or even distro environements doing basic performance tests (e.g.
> standardized benchmarks) then there is probably some other problem that
> we should be aware of. Most of the standardized benchmarks elimininate
> the variance of the underlying system to the best of their ability.
> For instance, kernbench carries around a full kernel (quite backlevel)
> as the kernel that it builds. The goal is to make sure that the kernel
> being built hasn't changed from one version to the next. In this case,
> it is also important to use the same compiler since there can be
> extensive variation between versions of gcc.
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Received on Mon Jul 10 12:14:37 2006