Re: Deactivating TCP checksumming

Re: Deactivating TCP checksumming

[shesha bhushan]

I get that. I can talk with the driver vendor. But to gain the usefulness of 
caculation of CSUM in HW we need to disable the software CSUM calculation in 
TCP layer in the kernel. Am I correct? I am trying to find that and I ma 
stuck there. How to disble the software TCP CSUM calculation? and later I 
can talk with driver vendor to enable it in hardware. I wanted help from 
linux gurus in disabling TCP csum calculation in the kernel.

Thanking You
Shesha






>From: Matti Aarnio <matti.aarnio@zmailer.org>
>To: shesha bhushan <bhushan_vadulas@hotmail.com>
>Subject: Re: Deactivating TCP checksumming
>Date: Tue, 1 Apr 2003 15:00:08 +0300
>
>On Tue, Apr 01, 2003 at 11:22:50AM +0000, shesha bhushan wrote:
> > Ok I will. Is there any other material which I can reffer?
> > I am using Intel pro1000 GBE
> >
> > Thank you very much for providing me the below information.
>
>You will need to talk with the driver author then.
>In 2.4.20 kernels (at least RedHat version) there is directory
>   drivers/net/e1000/
>in which the driver code resides.
>
>The  e1000_main.c  has:
>
>         if(adapter->hw.mac_type >= e1000_82543) {
>                 netdev->features = NETIF_F_SG |
>                                    NETIF_F_HW_CSUM |
>                                    NETIF_F_HW_VLAN_TX |
>                                    NETIF_F_HW_VLAN_RX |
>                                    NETIF_F_HW_VLAN_FILTER;
>         } else {
>                 netdev->features = NETIF_F_SG;
>         }
>
>
>   ... so, if your card isn't with that chip, then perhaps that is
>the reason for not doing checksums in HW ?
>
>Existence of that kind of test is telling to me, that "E1000" name
>is used to refer to a series of cards with varying properties.
>(Like there are a whole family of cards driven by  3c59x driver,
>  and even larger one referred as "tulip".)
>
>/Matti Aarnio
>
> > >From: Matti Aarnio <matti.aarnio@zmailer.org>
> > >To: shesha bhushan <bhushan_vadulas@hotmail.com>
> > >CC: linux-kernel@vger.kernel.org, kernelnewbies@nl.linux.org
> > >Subject: Re: Deactivating TCP checksumming
> > >Date: Tue, 1 Apr 2003 13:58:21 +0300
> > >
> > >On Tue, Apr 01, 2003 at 09:47:30AM +0000, shesha bhushan wrote:
> > >> Hello all,
> > >>  I am trying to de-activate the TCP checksumming and allow hardware 
>(GBE
> > >to
> > >> compute it for me). But can any one let me know how to do it.
> > >
> > >GBE ?  Likely device feature flags are wrong -- See examples
> > >from   drivers/net/sunhme.c,  acenic.c,  tg3.c  for various ways
> > >to use  NETIF_F_*_CSUM  feature flags.
> > >
> > >For (some of) explanations:  include/linux/netdevice.h
> > >(for NETIF_F_* flags)
> > >
> > >> All suggestion are highly apperciated.
> > >>
> > >> Thanking You
> > >> Shesha
> > >
> > >/Matti Aarnio


_________________________________________________________________

Re: Deactivating TCP checksumming

[Matti Aarnio]

On Tue, Apr 01, 2003 at 12:12:04PM +0000, shesha bhushan wrote:
> I get that. I can talk with the driver vendor. But to gain the usefulness 
> of caculation of CSUM in HW we need to disable the software CSUM 
> calculation in TCP layer in the kernel. Am I correct? I am trying to find 
> that and I ma stuck there. How to disble the software TCP CSUM calculation? 
> and later I can talk with driver vendor to enable it in hardware. I wanted 
> help from linux gurus in disabling TCP csum calculation in the kernel.

The kernel code is already smart enough of detect that the outbound
device will handle the checksum calculations all by itself, and not
do it in that case.

Testing of  dev->features   is done in files:
   net/core/dev.c
   net/ipv4/tcp.c
(depending what protocol is in question.)
in the latter case, actually in common tcp path with route-cached 
route_caps flags.

I did
   egrep 'NETIF_F_.._CSUM' net/*/*.c
to find those.
(and a number of other subset searches finding nothing)

Grep is your friend.

This whole "zero-copy" infastructure was implemented during
development in 2.3 series.

> Thanking You
> Shesha

/Matti Aarnio

Re: Deactivating TCP checksumming

[Dennis Cook]

Using RH Linux kernel 2.4.18, setting "features" bit NETIF_F_IP_CSUM does
not appear
to keep a valid IP checksum from being computed in packets presented to my
driver
for transmission. So having HW compute outgoing checksum buys nothing.
Checked this
by suppressing HW checksum computation. Packets are still accepted by peer.

Dennis Cook
Sandgate Technologies

"Matti Aarnio" <matti.aarnio@zmailer.org> wrote in message
news:20030401122824.GY29167@mea-ext.zmailer.org...
> On Tue, Apr 01, 2003 at 12:12:04PM +0000, shesha bhushan wrote:
> > I get that. I can talk with the driver vendor. But to gain the
usefulness
> > of caculation of CSUM in HW we need to disable the software CSUM
> > calculation in TCP layer in the kernel. Am I correct? I am trying to
find
> > that and I ma stuck there. How to disble the software TCP CSUM
calculation?
> > and later I can talk with driver vendor to enable it in hardware. I
wanted
> > help from linux gurus in disabling TCP csum calculation in the kernel.
>
> The kernel code is already smart enough of detect that the outbound
> device will handle the checksum calculations all by itself, and not
> do it in that case.
>
> Testing of  dev->features   is done in files:
>    net/core/dev.c
>    net/ipv4/tcp.c
> (depending what protocol is in question.)
> in the latter case, actually in common tcp path with route-cached
> route_caps flags.
>
> I did
>    egrep 'NETIF_F_.._CSUM' net/*/*.c
> to find those.
> (and a number of other subset searches finding nothing)
>
> Grep is your friend.
>
> This whole "zero-copy" infastructure was implemented during
> development in 2.3 series.
>
> > Thanking You
> > Shesha
>
> /Matti Aarnio

Re: Deactivating TCP checksumming

[Jeff Garzik]

On Wed, Apr 02, 2003 at 02:22:59PM -0500, Dennis Cook wrote:
> Using RH Linux kernel 2.4.18, setting "features" bit NETIF_F_IP_CSUM does
> not appear
> to keep a valid IP checksum from being computed in packets presented to my
> driver
> for transmission. So having HW compute outgoing checksum buys nothing.

You are not using sendfile(2), which is required to activate h/w csum.

	Jeff

Re: Deactivating TCP checksumming

[Dennis Cook]

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.

"Jeff Garzik" <jgarzik@pobox.com> wrote in message
news:20030402203653.GA2503@gtf.org...
> On Wed, Apr 02, 2003 at 02:22:59PM -0500, Dennis Cook wrote:
> > Using RH Linux kernel 2.4.18, setting "features" bit NETIF_F_IP_CSUM
does
> > not appear
> > to keep a valid IP checksum from being computed in packets presented to
my
> > driver
> > for transmission. So having HW compute outgoing checksum buys nothing.
>
> You are not using sendfile(2), which is required to activate h/w csum.
>
> Jeff
>
>
>

Re: Deactivating TCP checksumming

[Jeff Garzik]

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

Re: Deactivating TCP checksumming

[Richard B. Johnson]

On Wed, 2 Apr 2003, 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.
REALLY? Who are you kidding. Windows has no such capability.

Check \WINDOWS\SYSTEM32\DRIVERS\ETC\* and see who they stole
the TCP/IP stack from!

Further, when you perform normal user->TCP/IP operations, you
get checksumming for free as part of the copy operation. It's
only when you don't even copy data that you can get any advantage
of not checksumming. That's why sendfile disables it.

Cheers,
Dick Johnson
Penguin : Linux version 2.4.20 on an i686 machine (797.90 BogoMips).
Why is the government concerned about the lunatic fringe? Think about it.

Re: Deactivating TCP checksumming

[Dennis Cook]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 1957 bytes --]

Re: Windows support of checksum offloading (not kidding).

Following from Windows DDK

===============================================

To achieve a significant performance boost, the Microsoft TCP/IP transport
can offload one or more of the following tasks to a NIC that has the
appropriate task-offload capabilities:

  a.. Checksum tasks
  The TCP/IP transport can offload the calculation and/or validation of IP
and/or TCP checksums. The initial release of Windows® 2000 does not support
UDP checksum offloads; however, future service packs and update releases of
Windows 2000 and later versions may support UDP checksum offloads.


===============================================

Win2K SP3 and WinXP both indicate to my driver that TCP and IP checksums are
being offloaded
on packets to be sent provided the driver advertises that the associated HW
is capable of computing
the checksums. I haven't established that the SW transport stack actually
skips computing the checksums.

"Richard B. Johnson" <root@chaos.analogic.com> wrote in message
news:Pine.LNX.4.53.0304021555160.32710@chaos...
> On Wed, 2 Apr 2003, 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.
> REALLY? Who are you kidding. Windows has no such capability.
>
> Check \WINDOWS\SYSTEM32\DRIVERS\ETC\* and see who they stole
> the TCP/IP stack from!
>
> Further, when you perform normal user->TCP/IP operations, you
> get checksumming for free as part of the copy operation. It's
> only when you don't even copy data that you can get any advantage
> of not checksumming. That's why sendfile disables it.
>
> Cheers,
> Dick Johnson
> Penguin : Linux version 2.4.20 on an i686 machine (797.90 BogoMips).
> Why is the government concerned about the lunatic fringe? Think about it.
>

Re: Deactivating TCP checksumming

[Dennis Cook]

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
>
>

Re: Deactivating TCP checksumming

[Jeff Garzik]

Dennis Cook wrote:
> 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.

CHECKSUM_HW is for receive, not transmit.  Read the comments at the top 
of include/linux/skbuff.h.


> Is this mechanism possibly broken on kernel 2.4?


it works quite well.

	Jeff

RE: Deactivating TCP checksumming

[Dennis Cook]

In the 3c59x.c, e1000, and other adapter drivers, ip_summed is
what is being checked for value CHECKSUM_HW when sending
a packet.

> -----Original Message-----
> From: Jeff Garzik [mailto:jgarzik@pobox.com]
> Sent: Thursday, April 03, 2003 03:47 PM
> To: Dennis Cook
> Cc: linux-kernel@vger.kernel.org; kernelnewbies@nl.linux.org
> Subject: Re: Deactivating TCP checksumming
> 
> 
> Dennis Cook wrote:
> > 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.
> 
> CHECKSUM_HW is for receive, not transmit.  Read the comments at the top 
> of include/linux/skbuff.h.
> 
> 
> > Is this mechanism possibly broken on kernel 2.4?
> 
> 
> it works quite well.
> 
> 	Jeff
> 
> 
> 
> 

Re: Deactivating TCP checksumming

[Ion Badulescu]

On Thu, 3 Apr 2003 15:34:59 -0500, Dennis Cook <cook@sandgate.com> wrote:
> 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?

No, but you also need the scatter-gather bit to be set. Otherwise the 
network needs to perform at least one copy to linearize the skb, thus it 
will take the opportunity to checksum it at the same time so the 
hardware capability of the board is not used.

Ion

-- 
  It is better to keep your mouth shut and be thought a fool,
            than to open it and remove all doubt.

Re: Deactivating TCP checksumming

[Abhishek Agrawal]

On Fri, 2003-04-04 at 02:17, Jeff Garzik wrote:

>
> CHECKSUM_HW is for receive, not transmit.  Read the comments at the top
> of include/linux/skbuff.h.
>
Actually CHECKSUM_HW can be set at either of the "producer" ends. At
least this is what I gather from  tcp_output.c

// tcp_output.c:454
if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_HW) {
  //...
        }
else {
                skb->ip_summed = CHECKSUM_HW;
                skb_split(skb, buff, len);
     }

AND

//1014 dev.c:dev_queue_xmit()
        /* If packet is not checksummed and device does not support
         * checksumming for this protocol, complete checksumming here.
         */
        if (skb->ip_summed == CHECKSUM_HW &&
            (!(dev->features&(NETIF_F_HW_CSUM|NETIF_F_NO_CSUM)) &&
             (!(dev->features&NETIF_F_IP_CSUM) ||
              skb->protocol != htons(ETH_P_IP)))) {
                if ((skb = skb_checksum_help(skb)) == NULL)
                        return -ENOMEM;
        }

Re: Deactivating TCP checksumming

[Jeff Garzik]

Dennis Cook wrote:
> In the 3c59x.c, e1000, and other adapter drivers, ip_summed is
> what is being checked for value CHECKSUM_HW when sending
> a packet.


Yep; my mistake on that one.

Regardless, Ion and Manish picked up on what you were missed - the 
NETIF_F_SG bit.  And if your hardware can do 64-bit DMA, you'll want to 
set NETIF_F_HIGHDMA too.

	Jeff

Re: Deactivating TCP checksumming

[Matti Aarnio]

On Tue, Apr 01, 2003 at 09:47:30AM +0000, shesha bhushan wrote:
> Hello all,
>  I am trying to de-activate the TCP checksumming and allow hardware (GBE to 
> compute it for me). But can any one let me know how to do it.

GBE ?  Likely device feature flags are wrong -- See examples
from   drivers/net/sunhme.c,  acenic.c,  tg3.c  for various ways
to use  NETIF_F_*_CSUM  feature flags.

For (some of) explanations:  include/linux/netdevice.h
(for NETIF_F_* flags)

> All suggestion are highly apperciated.
> 
> Thanking You
> Shesha

/Matti Aarnio

Deactivating TCP checksumming

[shesha bhushan]

Hello all,
  I am trying to de-activate the TCP checksumming and allow hardware (GBE to 
compute it for me). But can any one let me know how to do it.

This is what I did.But Its not working for me.

In linux/net/ipv4/tcp.c there are function calls to 
csum_and_copy_from_user(). I replaced it from copy_from_user() and set the 
skb->ip_summed = CHECKSUM_HW and skb->csum = 1;. Is this correct. Since its 
not working there must be something more that has to be done. could any one 
please tell me what additional thinks I need to do.

All suggestion are highly apperciated.

Thanking You
Shesha




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