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Date:   Sun, 15 Oct 2017 08:51:22 +0000
From:   Yuval Mintz <yuvalm@...lanox.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "huangdaode@...ilicon.com" <huangdaode@...ilicon.com>,
        "xuwei5@...ilicon.com" <xuwei5@...ilicon.com>,
        "liguozhu@...ilicon.com" <liguozhu@...ilicon.com>,
        "Yisen.Zhuang@...wei.com" <Yisen.Zhuang@...wei.com>,
        "gabriele.paoloni@...wei.com" <gabriele.paoloni@...wei.com>,
        "john.garry@...wei.com" <john.garry@...wei.com>,
        "linuxarm@...wei.com" <linuxarm@...wei.com>,
        "salil.mehta@...wei.com" <salil.mehta@...wei.com>,
        "lipeng321@...wei.com" <lipeng321@...wei.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "amritha.nambiar@...el.com" <amritha.nambiar@...el.com>
Subject: RE: [PATCH net-next 0/2] Add mqprio hardware offload support in hns3
 driver

> > >> This patchset adds a new hardware offload type in mqprio before
> adding
> > >> mqprio hardware offload support in hns3 driver.

Apparently Dave has already accepted 	Amirtha's changes to mqprio:
https://marc.info/?l=linux-netdev&m=150803219824053&w=2 
so I guess you need to revise your patchs to align to the new conventions.

> > >
> > > I think one of the biggest issues in tying this to DCB configuration is the
> > > non-immediate [and possibly non persistent] configuration.
> > >
> > > Scenario #1:
> > > User is configuring mqprio offloaded with 3 TCs while device is in willing
> > mode.
> > > Would you expect the driver to immediately respond with a success or
> > instead
> > > delay the return until the DCBx negotiation is complete and the
> operational
> > > num of TCs is actually 3?
> >
> > Well, when user requsts the mqprio offloaded by a hardware shared by
> DCB,
> > I expect
> > the user is not using the dcb tool.
> > If user is still using dcb tool, then result is undefined.
> >
> > The scenario you mention maybe can be enforced by setting willing to zero
> > when user
> > is requesting the mqprio offload, and restore the willing bit when unloaded
> > the mqprio
> > offload.
> 
> Sounds a bit harsh but would probably work.
> 
> > But I think the real issue is that dcb and mqprio shares the tc system in the
> > stack,
> > the problem may be better to be fixed in the stack rather than in the
> driver,
> > as you
> > suggested in the DCB patchset. What do you think?
> 
> What did you have in mind?
> 
> >
> > >
> > > Scenario #2:
> > > Assume user explicitly offloaded mqprio with 3 TCs, but now DCB
> > configuration
> > > has changed on the peer side and 4 TCs is the new negotiated operational
> > value.
> > > Your current driver logic would change the number of TCs underneath
> the
> > user
> > > configuration [and it would actually probably work due to mqprio being a
> > crappy
> > > qdisc]. But was that the user actual intention?
> > > [I think the likely answer in this scenario is 'yes' since the alternative is no
> > better.
> > > But I still thought it was worth mentioning]
> >
> > You are right, the problem also have something to do with mqprio and dcb
> > sharing
> > the tc in the stack.
> >
> > Druing testing, when user explicitly offloaded mqprio with 3 TCs, all
> > queue has a default pfifo mqprio attached, after DCB changes the tc num
> to
> > 4,
> > using tc qdisc shows some queue does not have a default pfifo mqprio
> > attached.
> 
> Really? Then what did it show?
> [I assume it has some pfifo attached, and it's an mqprio dump kind of an
> issue]
> 
> >
> > Maybe we can add a callback to notify mqprio the configuration has
> changed.
> >
> 
> Which would do what?
> You already have the notifications available for monitoring using dcbnl logic if
> the
> configuration change [for user]; So user can re-configure whatever it wants.
> But other than dropping all the qdisc configurations and going back to the
> default
> qdiscs, what default action would mqprio be able to do when configuration
> changes
> that actually makes sense?
> 
> > Thanks
> > Yunsheng Lin
> >
> > >
> > > Cheers,
> > > Yuval
> > >
> > >>
> > >> Yunsheng Lin (2):
> > >>   mqprio: Add a new hardware offload type in mqprio
> > >>   net: hns3: Add mqprio hardware offload support in hns3 driver
> > >>
> > >>  drivers/net/ethernet/hisilicon/hns3/hnae3.h        |  1 +
> > >>  .../net/ethernet/hisilicon/hns3/hns3pf/hclge_dcb.c | 23 +++++++++++
> > >>  .../net/ethernet/hisilicon/hns3/hns3pf/hns3_enet.c | 46
> > ++++++++++++++-
> > >> -------
> > >>  include/uapi/linux/pkt_sched.h                     |  1 +
> > >>  4 files changed, 55 insertions(+), 16 deletions(-)
> > >>
> > >> --
> > >> 1.9.1
> > >
> > >
> > >

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