netdev - Re: [net-next V2 08/15] net/mlx5e: Add TX PTP port object support

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Message-ID: <20201204151743.4b55da5c@kicinski-fedora-pc1c0hjn.DHCP.thefacebook.com>
Date:   Fri, 4 Dec 2020 15:17:43 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Saeed Mahameed <saeed@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Eran Ben Elisha <eranbe@...dia.com>,
        Tariq Toukan <tariqt@...dia.com>
Subject: Re: [net-next V2 08/15] net/mlx5e: Add TX PTP port object support

On Fri, 04 Dec 2020 13:57:49 -0800 Saeed Mahameed wrote:
> > > option 2) route PTP traffic to a special SQs per ring, this SQ will
> > > be
> > > PTP port accurate, Normal traffic will continue through regular SQs
> > > 
> > > Pros: Regular non PTP traffic not affected.
> > > Cons: High memory footprint for creating special SQs
> > > 
> > > So we prefer (2) + private flag to avoid the performance hit and
> > > the
> > > redundant memory usage out of the box.  
> > 
> > Option 3 - have only one special PTP queue in the system. PTP traffic
> > is rather low rate, queue per core doesn't seem necessary.
> 
> We only forward ptp traffic to the new special queue but we create more
> than one to avoid internal locking as we will utilize the tx softirq
> percpu.

In other words to make the driver implementation simpler we'll have
a pretty basic feature hidden behind a ethtool priv knob and a number
of queues which doesn't match reality reported to user space. Hm.