David,
We are working on your comments. Will get back to you before end of
next week.
Thanks,
Ravi
-----Original Message-----
From: David S. Miller [mailto:davem@xxxxxxxxxxxxx]
Sent: Tuesday, July 19, 2005 2:23 PM
To: ravinandan.arakali@xxxxxxxxxxxx
Cc: jgarzik@xxxxxxxxx; netdev@xxxxxxxxxxx;
raghavendra.koushik@xxxxxxxxxxxx; leonid.grossman@xxxxxxxxxxxx;
ananda.raju@xxxxxxxxxxxx; rapuru.sriram@xxxxxxxxxxxx
Subject: Re: [PATCH 2.6.12-rc4] IPv4/IPv6: USO v2, Scatter-gather
approach
From: ravinandan.arakali@xxxxxxxxxxxx
Date: Thu, 2 Jun 2005 17:41:06 -0700 (PDT)
> Attached below is version 2 of kernel patch for UDP Large send offload
> feature. This patch uses the "Scatter-Gather" approach.
> It also incorporates David Miller's comments on the first version.
I've reviewed this patches, and I think there is a problem
with the sock_append_data() scheme. You disallow the case
where there is an SKB on the write queue already.
This breaks NFS, and other things using MSG_MORE and UDP_CORK.
They do a two step packet building:
1) Send protocol headers, f.e. NFS
2) Send file contents via sendfile()
3) Uncork socket so packet gets emitted
and due to this check:
+ if (skb_queue_len(&sk->sk_write_queue)) {
+ *err = -EOPNOTSUPP;
+ return NULL;
+ }
you end up not supporting this correctly.
So we have two options, either add support for corked socket
handling to sock_append_data() or we go with the frag_list
patch which doesn't have this problem.
I prefer the frag_list patch from a cleanliness perspective,
however I remember you saying that the sock_append_data()
approach obtained better performance. And that seems clear
since there will be less TX descriptors needed to send such
frames unless the driver does coalescing as it walks the
frag_list chain.
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