linux-kernel - Re: [PATCH net-next v3 08/11] net: ethernet: ti: cpts: move rx timestamp processing to ptp worker only

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Date:   Tue, 24 Mar 2020 09:54:14 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Grygorii Strashko <grygorii.strashko@...com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Lokesh Vutla <lokeshvutla@...com>,
        Tony Lindgren <tony@...mide.com>, Sekhar Nori <nsekhar@...com>,
        Murali Karicheri <m-karicheri2@...com>,
        netdev <netdev@...r.kernel.org>, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 08/11] net: ethernet: ti: cpts: move rx
 timestamp processing to ptp worker only

On Tue, Mar 24, 2020 at 05:34:34PM +0200, Grygorii Strashko wrote:
> I tested both ways and kept this version as i'v not seen any degradation,
> but, of course, i'll redo the test (or may be you can advise what test to run).

Measure the time delay from when the frame arrives in the stack until
that frame+RxTimestamp arrives in the application.  I expect the round
about way via kthread takes longer. 

> My thoughts were - network stack might not immediately deliver packet to the application

The network stack always delivers the packet, but you artificially
delay that delivery by calling netif_receive_skb() later on from
cpts_match_rx_ts().

> and PTP worker can be tuned (pri and smp_affinity),

That won't avoid the net softirq.

> resulted code will be more structured,

I am afraid people will copy this pattern in new drivers.  It really
does not make much sense.

Thanks,
Richard