netdev - Re: [PATCH 20/31]: pkt_sched: Perform bulk of qdisc destruction in RCU.

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Date:	Mon, 21 Jul 2008 11:17:16 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	jamal <hadi@...erus.ca>
Cc:	kaber@...sh.net, davem@...emloft.net, netdev@...r.kernel.org,
	johannes@...solutions.net, linux-wireless@...r.kernel.org
Subject: Re: [PATCH 20/31]: pkt_sched: Perform bulk of qdisc destruction in	RCU.

On Sun, Jul 20, 2008 at 10:33:57PM -0400, jamal wrote:
> 
> True. 
> But note: this is only during rule creation - once you create the
> rule (user space to kernel path), then no more hash table reference.
> Fast path has already a filter with actions attached, and is a mere
> pointer dereference.

Unfortunately the scenario that I wrote this for requires frequent
addition/removal.

> > We could do a dynamic table but so far I'm not convinced that
> > it's worth anybody's effort to implement :)
> 
> If user<->kernel performance insertion/deletion is important, it is
> worth it.

Only if you also want to share it :) In the end I patched it to
not share it which is much easier.

> For example:
> Dave implemented dynamic hash tables on xfrm (voip setup time with ipsec
> is a metric used in the industry in that case) . The only operational
> problem i had with xfrm was lack of an upper bound of how large a table
> can grow; i would rather user space be told ENOMEM than continuing to
> grow in some cases (I actually implemented a patch which put a stop
> after a certain number of sad/spd - but i dont expect hugs if i was to
> post it;->).

Of course if you're volunteering to write the dynamic hash table
for actions then I'd happily switch back to sharing :)

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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