netdev - Re: [PATCH 3/3] timekeeping: remove arch

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Message-ID: <20201018095137.GV1551@shell.armlinux.org.uk>
Date:   Sun, 18 Oct 2020 10:51:38 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/3] timekeeping: remove arch_gettimeoffset

On Thu, Oct 15, 2020 at 02:38:07PM +0200, Linus Walleij wrote:
> On Thu, Oct 15, 2020 at 11:53 AM Russell King - ARM Linux admin
> <linux@...linux.org.uk> wrote:
> 
> > Don't be misled. It was not a matter of "enough gritty people", it
> > was a matter that EBSA110 was blocking it.
> 
> I remember that EBSA110 was quite different in that it had this
> especially limited PIT timer, true that. At one point I even read
> up on the details of it and then forgot them :/

Yes, it was so basic that it required software to reprogram it on every
interrupt - it had no sensible periodic mode. The side effect of which
was that unless done carefully, your timekeeping varied all over the
place (so much that ntpd was not happy.) The final implementation made
ntpd really quite happy on the machine despite the timer's weirdness,
up until Linux stopped allowing interrupts to be nested. At that point,
it was back to utterly crap timekeeping.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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