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SubjectRe: Measured overhead of timer interrupts
On Fri, Jul 23, 1999 at 05:16:45AM +0200, Albert D. Cahalan wrote:
>
> Andi Kleen writes:
> > On Thu, Jul 22, 1999 at 09:12:22PM +0200, Khimenko Victor wrote:
> >> In <19990722171109.A1783@fred.muc.de> Andi Kleen (ak@muc.de) wrote:
> >>> On Thu, Jul 22, 1999 at 05:02:14PM +0200, Ingo Molnar wrote:
> >>>> On 22 Jul 1999, Andi Kleen wrote:
>
> >>>>> It is a kernel bug, HZ is not exported. Actually two,
> >>>>> because none of the /proc should have used it as units,
> >>>>> but that cannot be fixed anymore.
>
> One value alone is poor. We ought to have:
>
> CLOCKS_HZ for the one ugly system call
> PROC_HZ for general /proc output
> PROCNET_HZ for /proc/net specifically
> TRUE_HZ what the kernel really uses, even if not periodic
>
> >> /proc interface are in permanent change. We should keep it consistent
> >> in one stable kernel series but I see no reason to keep it consistent
> >> between major kernel updates: quite a lot of things will be changed anyway.
> >
> > This is not really true. There are new columns or lines added to /proc
> > files, but old ones are not changes, and correctly writen /proc parsers
> > should not break (unfortunately there are lots of incorrectly writen
> > proc parser around..)
>
> I know this is not true. I wrote the new ps. (prepare for rant)
> There is no way to write a parser that will survive all of:
>
> 1. new columns

It is handleable.

You wrote the code to parse:

Bla blub bli
1 2 3

the new kernel has

Bla blub blo bli
1 2 5 3

So in perl code (for compactness, C is only a bit wordier, untested, I'm
sure a perl guru could write it in less lines):

%known_titles = ("Bla" => -1, "blub" => -1, "bli" => -1);

# match known titles to column numbers.
$titleline = <PROCFH>;
@fields = split(/\s+/,$titleline);
$column = 0;
foreach (@fields) {
if ($known_titles{$_}) {
$known_titles{$_} = $column;
}
$column++;
}
# handling for missing columns is easy to add here.
#now read /proc file
while(<PROCFH>) {
@fields = split(/\s+/);
$bla = $fields[$known_titles{"Bla"}];
$bli = $fields[$known_titles{"bli"}];
$blub = $fields[$known_titles{"blub"}];
# process them..
}
> 2. new spelling for keywords or row names

That is simply a bug and should never happen.

> 3. new rows

New rows are easy. You have to deal with them all the times.

> 4. apparent keyword columns that suddenly get whitespace

???



-Andi
--
This is like TV. I don't like TV.

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