netdev - Re: [PATCH net-next 6/8] bnxt_en: Implement ethtool -X to set indirection table.

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Message-ID: <CACKFLin7DSADqfm8BjQxtM2sYZZV6Ycq_oHPT0+e53xpCoi1xA@mail.gmail.com>
Date:   Mon, 29 Jun 2020 17:38:33 -0700
From:   Michael Chan <michael.chan@...adcom.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     David Miller <davem@...emloft.net>, Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 6/8] bnxt_en: Implement ethtool -X to set
 indirection table.

On Mon, Jun 29, 2020 at 5:06 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Mon, 29 Jun 2020 02:34:22 -0400 Michael Chan wrote:
> > With the new infrastructure in place, we can now support the setting of
> > the indirection table from ethtool.
> >
> > The user-configured indirection table will need to be reset to default
> > if we are unable to reserve the requested number of RX rings or if the
> > RSS table size changes.
> >
> > Signed-off-by: Michael Chan <michael.chan@...adcom.com>
>
> Hm. Clearing IFF_RXFH_CONFIGURED seems wrong. The user has clearly
> requested a RSS mapping, if it can't be maintained driver should
> return an error from the operation which attempts to change the ring
> count.

Right.  In this case the user has requested non default RSS map and is
now attempting to change rings.  We have a first level check by
calling bnxt_check_rings().  Firmware will tell us if the requested
rings are available or not.  If not, we will return error and the
existing rings and RSS map will be kept.  This should be the expected
outcome in most cases.

In rare cases, firmware can return success during bnxt_check_rings()
but during the actual ring reservation, it fails to reserve all the
rings it promised were available earlier.  In this case, we fall back
and accept the fewer rings and set the RSS map to default.  I have
never seen this scenario but we need to put the code in just in case
it happens.  It should be rare.