Subject: Re: [EXTERNAL] Re: [PATCH V2,net-next, 1/2] net: mana: Add support for coalesced RX packets on CQE

From: Jakub Kicinski <[email-masked]>
Date: Mon, 12 Jan 2026 17:21:46 -0800

On Mon, 12 Jan 2026 21:01:59 +0000 Haiyang Zhang wrote:
> > > Our NIC can have up to 4 RX packets on 1 CQE. To support this feature,
> > > check and process the type CQE_RX_COALESCED_4. The default setting is
> > > disabled, to avoid possible regression on latency.
> > >
> > > And add ethtool handler to switch this feature. To turn it on, run:
> > >   ethtool -C <nic> rx-frames 4
> > > To turn it off:
> > >   ethtool -C <nic> rx-frames 1  
> > 
> > Exposing just rx frame count, and only two values is quite unusual.
> > Please explain in more detail the coalescing logic of the device.  
> Our NIC device only supports coalescing on RX. And when it's disabled each
> RX CQE indicates 1 RX packet; when enabled each RX CQE indicates up to 4 packets.

I get that. What is the logic for combining 4 packets into a single
completion? How does it work? Your commit message mentions "regression
on latency" - what is the bound on that regression?