linux-kernel - Re: [PATCH net-next 1/4] time64.h: define PSEC_PER

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Message-ID: <20220627085101.jw55y3fakqcw7zgi@skbuf>
Date:   Mon, 27 Jun 2022 08:51:02 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Michael Walle <michael@...le.cc>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Maxim Kochetkov <fido_max@...ox.ru>,
        Colin Foster <colin.foster@...advantage.com>,
        Richie Pearn <richard.pearn@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH net-next 1/4] time64.h: define PSEC_PER_NSEC and use it in
 tc-taprio

Hi Vincenzo,

On Mon, Jun 27, 2022 at 08:52:51AM +0100, Vincenzo Frascino wrote:
> Hi Vladimir,
> 
> On 6/26/22 13:05, Vladimir Oltean wrote:
> > Time-sensitive networking code needs to work with PTP times expressed in
> > nanoseconds, and with packet transmission times expressed in
> > picoseconds, since those would be fractional at higher than gigabit
> > speed when expressed in nanoseconds.
> > 
> > Convert the existing uses in tc-taprio to a PSEC_PER_NSEC macro.
> > 
> > Cc: Andy Lutomirski <luto@...nel.org>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Vincenzo Frascino <vincenzo.frascino@....com>
> > Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> > ---
> >  include/vdso/time64.h  | 1 +
> >  net/sched/sch_taprio.c | 4 ++--
> >  2 files changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/vdso/time64.h b/include/vdso/time64.h
> > index b40cfa2aa33c..f1c2d02474ae 100644
> > --- a/include/vdso/time64.h
> > +++ b/include/vdso/time64.h
> > @@ -6,6 +6,7 @@
> >  #define MSEC_PER_SEC	1000L
> >  #define USEC_PER_MSEC	1000L
> >  #define NSEC_PER_USEC	1000L
> > +#define PSEC_PER_NSEC	1000L
> 
> Are you planning to use this definition in the vdso library code? If not, you
> should define PSEC_PER_NSEC in "include/linux/time64.h". The vdso namespace
> should contain only the definitions shared by the implementations of the kernel
> and of the vdso library.

I am not. I thought it would be ok to preserve the locality of
definitions by placing this near the others of its kind, since a macro
doesn't affect the compiled vDSO code in any way. But if you prefer, I
can create a new mini-section in linux/time64.h. Any preference on where
exactly to place that definition within the file?