Re: [gentoo-dev] Gentoo Council Reminder for May 28

[Roy Bamford <neddyseagoon@gentoo.org>]

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On 2009.05.28 06:46, Tiziano Müller wrote:
[snip]
> I did some analysis on that. The result is that the the performance
> penalty of not having the EAPI not in the filename depends on various
> factors. But it is for sure that there is a performance penalty.
It needs to be quantified in the GLEP.
Nobody wants to trawl this list looking for it.

> 
[snip the process - its an implementaion detail]
> So, one of the main differences is: "reading one cache file" (if
> running
> unstable you can asssume you support the highest version, thus 
> reading
> only one cache file) vs. "reading all cache files".
> 
> I did some performance measurements based on that. I have 1507
> installed
> packages with 5541 different versions/revisions.
> 
> Reading from hot cache:
> 1507 files: ~50ms
> 5541 files: ~170ms
> 
> Reading from cold cache:
> 1507 files: ~2.8s
> 5541 files: ~6s
As I understand this, it may add six seconds to an emerge world while 
the dep tree is calculated. Lets say it takes an hour to do emerge 
world, the time has increased from 3600 seconds to 3606 seconds or a 
trivial 0.1666667%

We are clearly concentrating our efforts in wrong area, trying to 
reduce the six seconds.
> 
> I made a lot of assumptions here (neglecting seek between ebuild-dir
> and
> metadata-dir, other processes using the drive, 80 ebuilds from
> overlays
> where the ebuild would have to be read, etc.). But estimating from 
> the
> numbers above I'd say that a "emerge -uD world"/"paludis -i world"
> will
> be at least twice as slow, which I think is not acceptable.

You mean 0.3% (or less) of the emerge world time?

> 
> And I also don't understand your point of stating it's "bad design". 
> I mean: when coding you should "not optimize prematurely", but with
> eapi-in-ebuild it is against the other principle of "not pessimize
> prematurely" (Sutter/Alexandrescu: C++ Coding Standards).

Coding Standards (whatever language) are not relevant. My point comes 
from Systems Design, before your write the Systems Requirement Document 
and the System Implementation Plan and even the Top Level Design 
document. ... thats a long time before you write any code. 

I am against *all* and any metadata in the filename. Today, GLEP 55 
proposes the add the EAIP, tomorrow, there will be something else,
the day after another thing ... and all because allowing EAPI set the 
precedent.

You also make the error of assuming that with eapi-in-ebuild the 
currently suggested approaches to extracting the EAPI from the ebuild 
are the best and remain unchanged. Thats unlikely, as not a lot of work 
has been done it yet.
> 
> 
> -- 
> Tiziano Müller
> Gentoo Linux Developer, Council Member
> Areas of responsibility:
>   Samba, PostgreSQL, CPP, Python, sysadmin, GLEP Editor
> E-Mail   : dev-zero@gentoo.org
> GnuPG FP : F327 283A E769 2E36 18D5  4DE2 1B05 6A63 AE9C 1E30
> 

- -- 
Regards,

Roy Bamford
(NeddySeagoon) a member of
gentoo-ops
forum-mods
treecleaners
trustees
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