LARTC - Oct 2002 - Can I allocate memory dynamically when enqueue or dequeue? (adding some algorithms in kernel)

Hi, I''m adding a queuing disc. inside kernel. I am
confused that it seems few other qdiscs allocate
memory dynamically. Is it invalid to use memory calls
like molloc or just a suggest that do not use it
often? Thanks for your help.         bon

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jbonf wrote:
>     Hi, I''m adding a queuing disc. inside kernel. I am
> confused that it seems few other qdiscs allocate
> memory dynamically. Is it invalid to use memory calls
> like molloc
No, you can kmalloc(...,GPF_ATOMIC) in enqueue and dequeue
functions.
> or just a suggest that do not use it often?
As a general rule, enqueue and dequeue are performance-critical,
so if you can move processing elsewhere, that''s better. (E.g. if
you just need to allocate some scratch space, you might as well
do this at qdisc init time - calls to enqueue, dequeue, and
requeue are serialized through dev->queue_lock.)

Of course, kmalloc and kfree are reasonably fast, so if you
really need to use them, that''s no tragedy. I''d be more
worried
about the times it takes to do whatever you''re going to do with
that kmalloc''ed space ...

For more details on locking in traffic control and such, you may
want to read tc.ps in
ftp://icaftp.epfl.ch/pub/people/almesber/junk/tc-04FEB2001-0.tar.gz
it''s a bit old and also unfinished, but it should give you an
idea of how things are organized.

- Werner

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 / Werner Almesberger, Buenos Aires, Argentina         wa@almesberger.net /
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