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

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Message-ID: <YA3GazNlINcNUBXZ@lunn.ch>
Date:   Sun, 24 Jan 2021 20:11:39 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Stefan Chulski <stefanc@...vell.com>
Cc:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        "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>,
        "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 02:43:30PM +0000, Stefan Chulski wrote:
> > 
> > ----------------------------------------------------------------------
> > 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.

And if the link has been negotiated to 10Mbps? Or is the clock already
scaled to the link speed?

       Andrew