netdev - RE: [PATCH net-next] net: mana: Add support for jumbo frame

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Message-ID: <PH7PR21MB31165FB2F772DBEEF242DCF4CA809@PH7PR21MB3116.namprd21.prod.outlook.com>
Date:   Mon, 20 Mar 2023 15:14:32 +0000
From:   Haiyang Zhang <haiyangz@...rosoft.com>
To:     Leon Romanovsky <leon@...nel.org>
CC:     "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Paul Rosswurm <paulros@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        Long Li <longli@...rosoft.com>,
        "ssengar@...ux.microsoft.com" <ssengar@...ux.microsoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next] net: mana: Add support for jumbo frame



> -----Original Message-----
> From: Leon Romanovsky <leon@...nel.org>
> Sent: Monday, March 20, 2023 3:42 AM
> To: Haiyang Zhang <haiyangz@...rosoft.com>
> Cc: linux-hyperv@...r.kernel.org; netdev@...r.kernel.org; Dexuan Cui
> <decui@...rosoft.com>; KY Srinivasan <kys@...rosoft.com>; Paul Rosswurm
> <paulros@...rosoft.com>; olaf@...fle.de; vkuznets@...hat.com;
> davem@...emloft.net; wei.liu@...nel.org; edumazet@...gle.com;
> kuba@...nel.org; pabeni@...hat.com; Long Li <longli@...rosoft.com>;
> ssengar@...ux.microsoft.com; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH net-next] net: mana: Add support for jumbo frame
> 
> On Sun, Mar 19, 2023 at 02:27:44PM -0700, Haiyang Zhang wrote:
> > During probe, get the hardware allowed max MTU by querying the device
> > configuration. Users can select MTU up to the device limit. Also,
> > when XDP is in use, we currently limit the buffer size to one page.
> >
> > Updated RX data path to allocate and use RX queue DMA buffers with
> > proper size based on the MTU setting.
> >
> > Signed-off-by: Haiyang Zhang <haiyangz@...rosoft.com>
> > ---
> >  .../net/ethernet/microsoft/mana/mana_bpf.c    |  22 +-
> >  drivers/net/ethernet/microsoft/mana/mana_en.c | 229 ++++++++++++----
> --
> >  include/net/mana/gdma.h                       |   4 +
> >  include/net/mana/mana.h                       |  18 +-
> >  4 files changed, 183 insertions(+), 90 deletions(-)
> 
> <...>
> 
> > +static int mana_change_mtu(struct net_device *ndev, int new_mtu)
> > +{
> > +	unsigned int old_mtu = ndev->mtu;
> > +	int err, err2;
> > +
> > +	err = mana_detach(ndev, false);
> > +	if (err) {
> > +		netdev_err(ndev, "mana_detach failed: %d\n", err);
> > +		return err;
> > +	}
> > +
> > +	ndev->mtu = new_mtu;
> > +
> > +	err = mana_attach(ndev);
> > +	if (!err)
> > +		return 0;
> > +
> > +	netdev_err(ndev, "mana_attach failed: %d\n", err);
> > +
> > +	/* Try to roll it back to the old configuration. */
> > +	ndev->mtu = old_mtu;
> > +	err2 = mana_attach(ndev);
> 
> I second to Francois and agree with him that it is very questionable.
> If mana_attach() failed for first try, you should bail out and not
> retry with some hope that it will pass.
> 

Will consider. Thanks.