RELENG_4 -> 5 -> 6: significant performance regression

[Brian K. White]

----- Original Message ----- 
From: "Bartosz Fabianowski" <freebsd at chillt.de>
To: <ml at sd2i.com>
Cc: <freebsd-stable at freebsd.org>
Sent: Thursday, April 27, 2006 3:40 PM
Subject: Re: RELENG_4 -> 5 -> 6: significant performance regression


>> You wrote that Giant is needed in 6.0 and now you write it has been
>> removed.
>
> In 4.x, every UFS write requires the Giant lock. In 6.x, Giant is not 
> normally required, making file system operations faster. When you enable 
> QUOTA, you basically get back to the 4.x behavior where Giant is needed 
> for each write. This is why in 6.x UFS will normally be faster but if you 
> enable QUOTA, you lose the newly gained performance again.

In that case the test was correct the question stands at least on that 
point.
If quota isn't mpsafe yet, that's fine. It just means that performance 
should still be only about the same as on 4 while quota is enabled.
Removing a feature you had before is no answer to this question.
Removing an expensive new feature that didn't exist before could be.

Is it maybe simply some expected/known extra overhead that is ok because 
it's understood that it's only for a while, while mpsafe quota gets polished 
and no one is expected to switch production boxes over until after?
And once we have mpsafe quota we'll have a faster fs that still delivers the 
same features?

Brian K. White  --  brian at aljex.com  --  http://www.aljex.com/bkw/
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