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Re: [PATCH] select appropriate skb size in tcp_sendmsg when TSO is used

To: "David S. Miller" <davem@xxxxxxxxxxxxx>
Subject: Re: [PATCH] select appropriate skb size in tcp_sendmsg when TSO is used
From: Jeff Garzik <jgarzik@xxxxxxxxx>
Date: Thu, 28 Oct 2004 00:16:33 -0400
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>, thomas.spatzier@xxxxxxxxxx, netdev@xxxxxxxxxxx
In-reply-to: <20041026175553.55a1b72d.davem@davemloft.net>
References: <OF96546AB5.ACE12043-ONC1256F33.0027BC6B-C1256F33.002D4A6E@de.ibm.com> <E1CKE5P-0005SP-00@gondolin.me.apana.org.au> <20041020163510.6d13e9c7.davem@davemloft.net> <20041026111912.GA18095@gondor.apana.org.au> <20041026235126.GA4733@gondor.apana.org.au> <417EE3BB.6040902@pobox.com> <20041027000724.GA4869@gondor.apana.org.au> <20041027001531.GA29973@havoc.gtf.org> <20041027002209.GA5002@gondor.apana.org.au> <20041026175553.55a1b72d.davem@davemloft.net>
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David S. Miller wrote:
On Wed, 27 Oct 2004 10:22:09 +1000
Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> wrote:


On Tue, Oct 26, 2004 at 08:15:31PM -0400, Jeff Garzik wrote:

IMHO it is valid to disable SG without disabling checksums, no?

It's useless: The packet header is always in a separate memory location from the packet data, when using zerocopy sendfile(2).

When not using zerocopy sendfile, you are copying the data _anyway_.

I'm fine with adding this check. However I think that belongs in another patch since we don't check that in register_netdev currently.

Dave, what do you think?


I believe that allowing TX csum support without SG _is_
useful even though it is not _effective_.

It is quite desirable for a driver author to be able to
test out his TX csum offload support first, then add
SG support next.  Similarly, if a driver author suspects
some issues with either SG or TX csum support, he can
better isolate the problem if we allow this.

Jeff do you agree?


<shrug> it's never used that way in practice AFAIK, only used by confused sysadmins :)

I won't object if you preserve the behavior, but I still don't see much value in allowing it.

        Jeff



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