On 20.08.2013 05:13, Julian Elischer wrote:
On 8/20/13 6:38 AM, Peter Grehan wrote:
Hi Andre,
(moving to the more appropriate freebsd-net)
I'm sorry for ambushing but this stuff has to be done. I have provided
an alternative way of handling it and I'm happy to help you with your
use case to make it good for you and to prevent the mbuf system from
getting bloated and hackish again.
Sure. I'm not really upset since my code wasn't too far along, but with any
API, you never know
who consumers might be so it's always worth being proactive about announcing
it's removal.
Can you please describe your intended use of M_NOFREE to better understand
the shortcomings of the current mbuf systems and the additional advantages
of the M_NOFREE case?
I was looking at something similar to Linux's vhost-net, where a guest's
virtio ring would be
processed in-kernel. An mbuf chain with external buffers would be used to pass
guest tx buffer/len
segments directly into FreeBSD drivers.
The intent of M_NOFREE was to avoid small mbuf allocations/frees in what is a
hot path. This code
was intended to run at 10/40G.
Note this code isn't really generic - it would require interfaces to be
'owned' by the guest,
except that direct PCI-level pass-through wouldn't be needed.
If there's an alternative to M_NOFREE, I'd be more than happy to use that.
I think an alternative would be a reference counted version. we used to have
that and NetBSD had a
quite sophisticated mbuf system where there were multiple owners of mbufs..
they wouldn't be freed until the last one freed it but I don't remember the
details.
I just had a glance at the NetBSD mbuf system and it doesn't look convincing
either. There may be some serious scalability issues with this "ownership"
thing.
--
Andre
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