linux-kernel - RE: [EXT] Re: [PATCH v2 RFC net-next 08/18] net: mvpp2: add FCA periodic timer configurations

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Date:   Sun, 24 Jan 2021 14:43:30 +0000
From:   Stefan Chulski <stefanc@...vell.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "thomas.petazzoni@...tlin.com" <thomas.petazzoni@...tlin.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Nadav Haklai <nadavh@...vell.com>,
        Yan Markman <ymarkman@...vell.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "mw@...ihalf.com" <mw@...ihalf.com>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "atenart@...nel.org" <atenart@...nel.org>
Subject: RE: [EXT] Re: [PATCH v2 RFC net-next 08/18] net: mvpp2: add FCA
 periodic timer configurations

> 
> ----------------------------------------------------------------------
> On Sun, Jan 24, 2021 at 01:43:57PM +0200, stefanc@...vell.com wrote:
> > +/* Set Flow Control timer x140 faster than pause quanta to ensure
> > +that link
> > + * partner won't send taffic if port in XOFF mode.
> 
> Can you explain more why 140 times faster is desirable here? Why 140 times
> and not, say, 10 times faster? Where does this figure come from, and what is
> the reasoning? Is there a switch that requires it?

I tested with 140.
Actually regarding to spec each quanta should be equal to 512 bit times.
In 10G bit time is 0.1ns.
So It actually should be:
FC_CLK_DIVIDER = 10000 / 512 = ~20. I took some buffer and made it 140.
So maybe I can do it 100?

Regards,
Stefan.