Re: Merging relayfs?

[Tomasz Kłoczko <kloczek@rudy.mif.pg.gda.pl>]

On Tue, 12 Jul 2005, Tom Zanussi wrote:

> =?ISO-8859-2?Q?Tomasz_K=B3oczko?= writes:
> > On Mon, 11 Jul 2005, Tom Zanussi wrote:
> >
> > >
> > > Hi Andrew, can you please merge relayfs?  It provides a low-overhead
> > > logging and buffering capability, which does not currently exist in
> > > the kernel.
> > >
> > > relayfs key features:
> > >
> > > - Extremely efficient high-speed logging/buffering
> >
> > Usualy/for now relayfs is used as base infrastructure for variuos
> > debuging/measuring.
> > IMO storing raw data and transfer them to user space it is wrong way.
> > Why ? Becase i adds very big overhead for memory nad storage.
> > Big .. compare to in situ storing partialy analyzed data in conters
> > and other like it is in DTrace.
> >
>
> But isn't it supposed to be a good thing to keep analysis out of the
> kernel if possible?

As long as you try for example measure (?) .. not.

> And many things can't be aggregated, such as the detailed sequence of 
> events in a trace.

DTrace real examples shows something completly diffret.
MANY things (if not ~almost all) can be kept only in aggregated form 
during experiments.

> Anyway, it doesn't have to be
> an 'all or nothing' thing.  For some applications it may make sense to
> do some amount of filtering and aggregation in the kernel.  AFAICS
> DTrace takes this to the extreme and does everything in the kernel,
> and IIRC it can't easily be made to general system tracing along the
> lines of LTT, for instance.

Try measure number of dysk I/O operation without touching storage for 
store raw data. What you need ? only one counter (few bytes) instead of huge 
amount of memeory for buffer and store logs. Try measure something like
scheduler with possible small system distruption.

kloczek
--
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*Ludzie nie mają problemów, tylko sobie sami je stwarzają*
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Tomasz Kłoczko, sys adm @zie.pg.gda.pl|*e-mail: kloczek@rudy.mif.pg.gda.pl*