netdev - Re: [PATCH v5 2/2] virtio-net: use mtu size as buffer length for big packets

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Date:   Wed, 7 Sep 2022 15:37:46 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Parav Pandit <parav@...dia.com>
Cc:     Gavin Li <gavinl@...dia.com>,
        "stephen@...workplumber.org" <stephen@...workplumber.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "jesse.brandeburg@...el.com" <jesse.brandeburg@...el.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "sridhar.samudrala@...el.com" <sridhar.samudrala@...el.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "loseweigh@...il.com" <loseweigh@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "virtio-dev@...ts.oasis-open.org" <virtio-dev@...ts.oasis-open.org>,
        Gavi Teitz <gavi@...dia.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Si-Wei Liu <si-wei.liu@...cle.com>
Subject: Re: [PATCH v5 2/2] virtio-net: use mtu size as buffer length for big
 packets

On Wed, Sep 07, 2022 at 03:36:16PM -0400, Michael S. Tsirkin wrote:
> On Wed, Sep 07, 2022 at 07:27:16PM +0000, Parav Pandit wrote:
> > 
> > > From: Michael S. Tsirkin <mst@...hat.com>
> > > Sent: Wednesday, September 7, 2022 3:24 PM
> > > 
> > > On Wed, Sep 07, 2022 at 07:18:06PM +0000, Parav Pandit wrote:
> > > >
> > > > > From: Michael S. Tsirkin <mst@...hat.com>
> > > > > Sent: Wednesday, September 7, 2022 3:12 PM
> > > >
> > > > > > Because of shallow queue of 16 entries deep.
> > > > >
> > > > > but why is the queue just 16 entries?
> > > > I explained the calculation in [1] about 16 entries.
> > > >
> > > > [1]
> > > >
> > > https://lore.kernel.org/netdev/PH0PR12MB54812EC7F4711C1EA4CAA119DC
> > > 419@
> > > > PH0PR12MB5481.namprd12.prod.outlook.com/
> > > >
> > > > > does the device not support indirect?
> > > > >
> > > > Yes, indirect feature bit is disabled on the device.
> > > 
> > > OK that explains it.
> > 
> > So can we proceed with v6 to contain 
> > (a) updated commit message and
> > (b) function name change you suggested to drop _fields suffix?
> 
> (c) replace mtu = 0 with sensibly not calling the function
> when mtu is unknown.
> 
> 
> And I'd like commit log to include results of perf testing
> - with indirect feature on
> - with mtu feature off
> just to make sure nothing breaks.

and if possible a larger ring. 1k?

> -- 
> MST