netdev - RE: [Patch v3] net: mana: Batch ringing RX queue doorbell on receiving packets

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Date: Thu, 6 Jul 2023 17:51:47 +0000
From: Long Li <longli@...rosoft.com>
To: Paolo Abeni <pabeni@...hat.com>, Jakub Kicinski <kuba@...nel.org>
CC: Greg KH <gregkh@...uxfoundation.org>, "longli@...uxonhyperv.com"
	<longli@...uxonhyperv.com>, Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky
	<leon@...nel.org>, Ajay Sharma <sharmaajay@...rosoft.com>, Dexuan Cui
	<decui@...rosoft.com>, KY Srinivasan <kys@...rosoft.com>, Haiyang Zhang
	<haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [Patch v3] net: mana: Batch ringing RX queue doorbell on
 receiving packets

> Subject: Re: [Patch v3] net: mana: Batch ringing RX queue doorbell on receiving
> packets
> 
> On Sun, 2023-07-02 at 20:18 +0000, Long Li wrote:
> > > > > > > > > Subject: Re: [Patch v3] net: mana: Batch ringing RX
> > > > > > > > > queue doorbell on receiving packets
> > > > > > > > >
> > > > > > > > > On Fri, 30 Jun 2023 20:42:28 +0000 Long Li wrote:
> > > > > > > > > > > > > > > > > > > > > 5.15 and kernel 6.1. (those
> > > > > > > > > > > > > > > > > > > > > kernels are longterm) They need
> > > > > > > > > > > > > > > > > > > > > this fix to achieve the
> > > > > > > > > > > > > > > > > > > > > performance target.
> > > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > > Why can't they be upgraded to get that
> > > > > > > > > > > > > > > > > performance target, and all the other
> > > > > > > > > > > > > > > > > goodness that those kernels have? We
> > > > > > > > > > > > > > > > > don't normally backport new features,
> > > > > > > > > > > > > > > > > right?
> > > > > > > > > > > > >
> > > > > > > > > > > > > I think this should be considered as a fix, not
> > > > > > > > > > > > > a new feature.
> > > > > > > > > > > > >
> > > > > > > > > > > > > MANA is designed to be 200GB full duplex at the
> > > > > > > > > > > > > start. Due to lack of hardware testing
> > > > > > > > > > > > > capability at early stage of the project, we
> > > > > > > > > > > > > could only test 100GB for the Linux driver. When
> > > > > > > > > > > > > hardware is fully capable of reaching designed
> > > > > > > > > > > > > spec, this bug in the Linux driver shows up.
> > > > > > > > >
> > > > > > > > > That part we understand.
> > > > > > > > >
> > > > > > > > > If I were you I'd try to convince Greg and Paolo that
> > > > > > > > > the change is small and significant for user experience.
> > > > > > > > > And answer Greg's question why upgrading the kernel past
> > > > > > > > > 6.1 is a challenge in your environment.
> > > > >
> > > > > I was under the impression that this patch was considered to be
> > > > > a feature, not a bug fix. I was trying to justify that the
> > > > > "Fixes:" tag was needed.
> > > > >
> > > > > I apologize for misunderstanding this.
> > > > >
> > > > > Without this fix, it's not possible to run a typical workload
> > > > > designed for 200Gb physical link speed.
> > > > >
> > > > > We see a large number of customers and Linux distributions
> > > > > committed on 5.15 and 6.1 kernels. They planned the product
> > > > > cycles and certification processes around these longterm kernel
> > > > > versions. It's difficult for them to upgrade to newer kernel
> > > > > versions.
> 
> I think there are some misunderstanding WRT distros and stable kernels.
> (Commercial) distros will backport the patch as needed, regardless such patch
> landing in the 5.15 upstream tree or not. Individual users running their own
> vanilla 5.15 kernel can't expect performance improvement landing there.
> 
> All in all I feel undecided. I would endorse this change going trough net-next
> (without the stable tag). I would feel less torn with this change targeting -net
> without the stable tag. Targeting -net with the stable tag sounds a bit too much to
> me.
> 
> Cheers,
> Paolo

I'm sending this patch to net-next without stable tag.

Thanks,

Long