Re: Undocumented and duplicated code

[Rene Herman]

On 07-05-08 14:46, Adrian Bunk wrote:

> > others like to to whitebox methods, ..., please try attach patch to
> > see if duron support PAT.
>
>
> There surely is documentation available covering this?
>
> And why do we need this clear_cpu_cap(c, X86_FEATURE_PAT) and then 
> manual setting of X86_FEATURE_PAT at all?
>
> There's no indication in the code, and as Rene already says there's even
> no description at all in commit 9307cacad0dfe3749f00303125c6f7f0523e5616
>
> Such code really needs a comment explaining why we have to do this at all.
>
> There must be some CPUs with the "pat" flag set but not being usable?
> Which?
>
> According to the linux-kernel discussions there might not be any broken 
> CPU at all - but in this case the whitelist will not fill itself, and 
> expecting people to note that their flags changed and complaining is not 
> really a good approach.

I'd say it's an insane approach unless there's actually some indication of
buggy CPUs. Which there might be, I don't know, but this then definitely
wants a comment and changelog.

Just now sent out another reply as well saying much the same:

http://marc.info/?l=linux-kernel&m=121016531804511&w=2

but I see you tracked the people involved and added them to CC on this
thread-leaf...

> And that your commit added the same clear/set code in three different 
> places doesn't look good - this really deserved from the beginning being 
> factored out into an own function to avoid future problems when CPUs get 
> added (like what happens with your patch here - it touches only one 
> place, and since the same context is present in two places in the same 
> file "patch" might even choose freely where it gets applied...).
>
> Pavel even made a similar comment on linux-kernel before the patch 
> got merged into Linus' tree. [1]
>
> Guys, even if it compiles in all randconfig configurations and works on 
> all test machines this is exactly the kind of stuff that causes 
> headaches in the future.
>
> And this patch (by the author of the code himself) is the first time 
> where it breaks.

Rene.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/