netdev - Re: [PATCH net-next 0/5] virtio-net: Add SCTP checksum offload support

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Message-ID: <20180418013333.GO4716@localhost.localdomain>
Date:   Tue, 17 Apr 2018 22:33:33 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Vlad Yasevich <vyasevic@...hat.com>
Cc:     Vladislav Yasevich <vyasevich@...il.com>, netdev@...r.kernel.org,
        linux-sctp@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, mst@...hat.com,
        jasowang@...hat.com, nhorman@...driver.com,
        Xin Long <lucien.xin@...il.com>
Subject: Re: [PATCH net-next 0/5] virtio-net: Add SCTP checksum offload
 support

On Tue, Apr 17, 2018 at 04:35:18PM -0400, Vlad Yasevich wrote:
> On 04/02/2018 10:47 AM, Marcelo Ricardo Leitner wrote:
> > On Mon, Apr 02, 2018 at 09:40:01AM -0400, Vladislav Yasevich wrote:
> >> Now that we have SCTP offload capabilities in the kernel, we can add
> >> them to virtio as well.  First step is SCTP checksum.
> >
> > Thanks.
> >
> >> As for GSO, the way sctp GSO is currently implemented buys us nothing
> >> in added support to virtio.  To add true GSO, would require a lot of
> >> re-work inside of SCTP and would require extensions to the virtio
> >> net header to carry extra sctp data.
> >
> > Can you please elaborate more on this? Is this because SCTP GSO relies
> > on the gso skb format for knowing how to segment it instead of having
> > a list of sizes?
> >
>
> it's mainly because all the true segmentation, placing data into chunks,
> has already happened.  All that GSO does is allow for higher bundling
> rate between VMs. If that is all SCTP GSO ever going to do, that fine,
> but the goal is to do real GSO eventually and potentially reduce the
> amount of memory copying we are doing.
> If we do that, any current attempt at GSO in virtio would have to be
> depricated and we'd need GSO2 or something like that.
>
> This is why, after doing the GSO support, I decided not to include it.

Gotcha. I don't think it will ever go further than what we have now.
Placing data into chunks later is not really feasible/wanted,
especially now with stream schedulers and idata chunks. Doesn't seem
worth the hassle... we would have to support things like, "segment
half of this message plus a third of this other one from that other
stream." (in case it's round robin).

  Marcelo