Messages in this thread | | | From | "Dennis Cook" <> | Subject | Re: Deactivating TCP checksumming | Date | Thu, 3 Apr 2003 15:34:59 -0500 |
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Based on various feedback, on my RH Linux 2.4.18 kernel I tried the following:
Set "features" bit NETIF_F_IP_CSUM set (the only feature bit set). In my network driver start-transmit check for "CHECKSUM_HW" in ip_summed. Using a small test program, use "sendfile" to copy a file to a network socket FD. Result is none of the packets presented to my network adapter driver have ip_summed set to CHECKSUM_HW, so the SW IP stack has already computed checksums.
Is this mechanism possibly broken on kernel 2.4?
"Jeff Garzik" <jgarzik@pobox.com> wrote in message news:20030402205855.GA4125@gtf.org... > On Wed, Apr 02, 2003 at 03:47:35PM -0500, Dennis Cook wrote: > > What I was looking for is a general capability to keep the SW transport > > stack from > > computing outgoing TCP/UDP/IP checksums so that the HW can be allowed to do > > it, > > similar to Windows checksum offload capability. > > If you are not using sendfile(2), it is _more expensive_ to offload > checksums, because we already checksum and copy at the same time. > > Hardware checksum offload is only a win when a copy is eliminated. > > Therefore, _always_ offloading checksum is actually slower in some > cases, because of the unneeded additional HW csum setup that would be > performed. > > Jeff > >
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