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Message-ID: <50a8ec7dece0100c931fd187e19e14dd1ca1a0e9.camel@redhat.com>
Subject: Re: [PATCH net-next v2 1/2] r8152: remove queuing rx packets in
 driver
From:   Paolo Abeni <pabeni@redhat.com>
To:     Hayes Wang <hayeswang@realtek.com>, Andrew Lunn <andrew@lunn.ch>
Cc:     "kuba@kernel.org" <kuba@kernel.org>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        nic_swsd <nic_swsd@realtek.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "edumazet@google.com" <edumazet@google.com>,
        "bjorn@mork.no" <bjorn@mork.no>
Date:   Thu, 21 Sep 2023 15:39:15 +0200
In-Reply-To: <1a57cf3f867d4dfd991ef1d4024c931b@realtek.com>
References: <20230919031351.7334-429-nic_swsd@realtek.com>
         <20230919031351.7334-430-nic_swsd@realtek.com>
         <369f3139-4e63-4327-8745-2d72d7dfea8f@lunn.ch>
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On Tue, 2023-09-19 at 12:26 +0000, Hayes Wang wrote:
> Andrew Lunn <andrew@lunn.ch>
> > Sent: Tuesday, September 19, 2023 8:08 PM
> [...]
> > > -     return work_done;
> > > +     if (work_done > budget)
> > > +             return budget;
> > > +     else
> > > +             return work_done;
> > >  }
> >=20
> > I don't know NAPI too well. Are there implications of not telling it
> > the truth?
>=20
> You could check the reply from Jakub Kicinski, as following link.
> https://www.spinics.net/lists/netdev/msg933846.html
> https://www.spinics.net/lists/netdev/msg933923.html
>=20
> If the work_done is more than budget, I should return budget.

One of the key points in Jakub's reply is that the burst must exceed
the budget by a limited number of packets:

"Nothing will explode if we process a few more packets than budget
(assuming budget > 0)"

How many packets can contain at most a single URB?

If that number can be significant greater then the napi budget, I think
we are better off keeping the packet in the queue - otherwise the whole
system latency/stability would be affected.

Cheers,

Paolo