> -----Original Message-----
> From: Jakub Kicinski <[email protected]>
> Sent: Saturday, January 17, 2026 5:49 PM
> To: Haiyang Zhang <[email protected]>
> Cc: Haiyang Zhang <[email protected]>; linux-
> [email protected]; [email protected]; KY Srinivasan
> <[email protected]>; Wei Liu <[email protected]>; Dexuan Cui
> <[email protected]>; Long Li <[email protected]>; Andrew Lunn
> <[email protected]>; David S. Miller <[email protected]>; Eric
> Dumazet <[email protected]>; Paolo Abeni <[email protected]>; Konstantin
> Taranov <[email protected]>; Simon Horman <[email protected]>; Erni
> Sri Satya Vennela <[email protected]>; Shradha Gupta
> <[email protected]>; Saurabh Sengar
> <[email protected]>; Aditya Garg
> <[email protected]>; Dipayaan Roy
> <[email protected]>; Shiraz Saleem
> <[email protected]>; [email protected]; linux-
> [email protected]; Paul Rosswurm <[email protected]>
> Subject: Re: [EXTERNAL] Re: [PATCH V2,net-next, 1/2] net: mana: Add
> support for coalesced RX packets on CQE
>
> On Sat, 17 Jan 2026 18:01:18 +0000 Haiyang Zhang wrote:
> > > > Since this feature is not common to other NICs, can we use an
> > > > ethtool private flag instead?
> > >
> > > It's extremely common. Descriptor writeback at the granularity of one
> > > packet would kill PCIe performance. We just don't have uAPI so NICs
> > > either don't expose the knob or "reuse" another coalescing param.
> >
> > I see. So how about adding a new param like below to "ethtool -C"?
> > ethtool -C|--coalesce devname [rx-cqe-coalesce on|off]
>
> I don't think we need on / off, just the params.
> If someone needs on / off setting - the size to 1 is basically off.
Ok --
I will add a numerical param "rx-cqe-frames" to "ethtool -C":
ethtool -C|--coalesce devname [rx-cqe-frames N]
//Accepts 1 or 4 frames/CQE for this NIC
>
> > > > When the flag is set, the CQE coalescing will be enabled and put
> > > > up to 4 pkts in a CQE. support
> > > > Does the "size" mean the max pks per CQE (1 or 4)?
> > [...]
> >
> > In "ethtool -c" output, add a new value like this?
> > rx-cqe-frames: (1 or 4 frames/CQE for this NIC)
>
> SG
Thanks.
> > > > The timeout value is not even exposed to driver, and subject to
> change
> > > > in the future. Also the HW mechanism is proprietary... So, can we
> not
> > > > "expose" the timeout value in "ethtool -c" outputs, because it's not
> > > > available at driver level?
> > >
> > > Add it to the FW API and have FW send the current value to the driver?
> >
> > I don't know where is the timeout value in the HW / FW layers. Adding
> > new info to the HW/FW API needs other team's approval, and their work,
> > which will need a complex process and a long time.
> >
> > > You were concerned (in the commit msg) that there's a latency cost,
> > > which is fair but I think for 99% of users 2usec is absolutely
> > > not detectable (it takes longer for the CPU to wake). So I think it'd
> > > be very valuable to the user to understand the order of magnitude of
> > > latency we're talking about here.
> >
> > For now, may I document the 2us in the patch description? And add a
> > new item to the "ethtool -c" output, like "rx-cqe-usecs", label is as
> > "n/a" for now, while we work out with other teams on the time value
> > API at HW/FW layers? So, this CQE coalescing feature support won't be
> > blocked by this "2usec" info API for a long time?
>
> Please do it right. We are in no rush upstream. It can't be that hard
> to add a single API to the FW within a single organization..
I will discuss this with our HW/FW teams.
Thanks,
- Haiyang
