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

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Date:   Sun, 2 Jul 2023 20:18:25 +0000
From:   Long Li <longli@...rosoft.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     Greg KH <gregkh@...uxfoundation.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "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 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.

Thanks,

Long