Re: Is ib_mtu iboe_get_mtu() slightly off?

[Leon Romanovsky <leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

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On Mon, Oct 09, 2017 at 09:34:33AM -0400, Doug Ledford wrote:
> On Thu, 2017-09-21 at 02:20 +0000, Parav Pandit wrote:
> > > From: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org [mailto:linux-rdma-
> > > owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org] On Behalf Of Roland Dreier
> > > Sent: Wednesday, September 20, 2017 7:39 PM
> > > To: linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> > > Subject: Is ib_mtu iboe_get_mtu() slightly off?
> > >
> > > We have:
> > >
> > > static inline enum ib_mtu iboe_get_mtu(int mtu) {
> > >         /*
> > >          * reduce IB headers from effective IBoE MTU. 28 stands for
> > >          * atomic header which is the biggest possible header after
> > > BTH
> > >          */
> > >         mtu = mtu - IB_GRH_BYTES - IB_BTH_BYTES - 28;
> > >        ...
> > >
> > > 28 bytes is the size of the AtomicETH header.  But couldn't we have
> > > a packet
> > > with both AtomicETH and XRCETH (4 more bytes)?
> >
> > XRCETH + AtomicETH is possible.
> > Additionally I guess 4 bytes of ICRC is missing too in calculation.
>
> Since no one rolled a patch for this, I did.
>

Doug,

Parav created, I waited for our shared code.
https://git.kernel.org/pub/scm/linux/kernel/git/leon/linux-rdma.git/commit/?h=rdma-next&id=51ed6735dd59008aea4d7308416ed994b277f168

commit 51ed6735dd59008aea4d7308416ed994b277f168
Author: Parav Pandit <parav-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Date:   Thu Oct 5 10:33:12 2017 -0500

    IB/core: Take into account optional XRC header and mandatory ICRC for RoCE MTU

    This fix considers optional XRC header size and mandatory ICRC 4 bytes in
    calculation of path MTU, by considering additional 8 bytes, path MTU calculation
    is more accurate.

    Link: https://www.spinics.net/lists/linux-rdma/msg54558.html
    Fixes: 3c86aa70bf67 ("RDMA/cm: Add RDMA CM support for IBoE devices")
    Signed-off-by: Parav Pandit <parav-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
    Reviewed-by: Daniel Jurgens <danielj-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
    Reported-by: Roland Dreier <roland-BHEL68pLQRGGvPXPguhicg@public.gmane.org>
    Signed-off-by: Leon Romanovsky <leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>

Thanks

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