linux-kernel - RE: [PATCH net-next v2 1/2] r8152: remove queuing rx packets in driver

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Date:   Fri, 22 Sep 2023 05:11:05 +0000
From:   Hayes Wang <hayeswang@...ltek.com>
To:     Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew@...n.ch>
CC:     "kuba@...nel.org" <kuba@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        nic_swsd <nic_swsd@...ltek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "bjorn@...k.no" <bjorn@...k.no>
Subject: RE: [PATCH net-next v2 1/2] r8152: remove queuing rx packets in driver

Paolo Abeni <pabeni@...hat.com>
> Sent: Thursday, September 21, 2023 9:39 PM
[...]
> 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?

I think it depends on
1. if the packets coming continually
2. the size of the packet

The URB would be completed when
1. the device doesn't receive any packet during several us.
2. the desired size is reached.

For 2.5G NIC with the packets of 1514 bytes, a urb at most contains about 21 packets.
If all packet are 60 bytes, the number would be about 390.
If the average size of the packets is 488 bytes, the number is about 64.

> 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.

Should I go back the patch with queuing the rx packet in driver?

Best Regards,
Hayes