netdev - RE: Drivers: net: Hyperv

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Date:	Tue, 22 Apr 2014 19:07:16 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Ben Hutchings <ben@...adent.org.uk>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"jasowang@...hat.com" <jasowang@...hat.com>
Subject: RE: Drivers: net: Hyperv



> -----Original Message-----
> From: Ben Hutchings [mailto:ben@...adent.org.uk]
> Sent: Tuesday, April 22, 2014 11:22 AM
> To: KY Srinivasan
> Cc: davem@...emloft.net; netdev@...r.kernel.org; olaf@...fle.de;
> jasowang@...hat.com
> Subject: Re: Drivers: net: Hyperv
> 
> On Tue, 2014-04-22 at 11:22 -0700, K. Y. Srinivasan wrote:
> > I am trying to port the various offloads (checksum, TSO etc.) that I
> > recently implemented for the Hyper-V network driver to a 2.6.32 kernel
> > and while this code works on the upstream bits, TCP checksum offload
> > does not seem to work on the 2.6.32 kernel. Would you know if there is
> > a different way to turn on checksum offload on 2.6.32 kernels?  I am setting
> the relevant feature flags:
> >
> >
> >         net->features =  NETIF_F_SG | NETIF_F_RXCSUM |
> >                         NETIF_F_IP_CSUM | NETIF_F_TSO;
> 
> There is no NETIF_F_RXCSUM in 2.6.32, but otherwise this should work.
> 
> I notice that NETIF_F_HIGHDMA is not there, and it seems like you could add
> it as netvsc_start_xmit() doesn't assume page fragments are in lowmem.

Ben,

Thank you for the prompt response. I added the HIGHDMA feature 
and yet I see the same behavior.

> 
> > What I am observing is that when the skb is presented to the driver
> > for transmission, The ip_summed field in the skb is set to 0.
> 
> Maybe you tested on a 32-bit system and the packet had to be copied to
> lowmem?  The allocation behaviour may have changed since 2.6.32.

I am testing on a 64 bit VM.

> 
> > On the kernel tip, I see this value set to CHECKSUM_PARTIAL and the
> > offloads work correctly on the kernel tip. The other difference I see
> > is that on entry into the driver, the eth_hdr state is not correctly set in the
> skb.
> > I need to invoke skb_reset_mac_header() to get this state correctly set.
> > Any help would be greatly appreciated.
> 
> I don't recall that problem.

Regards,

K. Y