Date: Mon, 9 Sep 2019 19:45:01 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: "O'Connor, Daniel" <darius@dons.net.au> Cc: Ian Lepore <ian@freebsd.org>, "usb@freebsd.org" <usb@FreeBSD.org>, "freebsd-arm@FreeBSD.org" <freebsd-arm@FreeBSD.org> Subject: Re: Is it a good idea to use a usb-serial adapter for PPS input? Yes, it is. Message-ID: <20190909164501.GT2559@kib.kiev.ua> In-Reply-To: <25BF53F1-23CF-4619-AB13-110566D6DC82@dons.net.au> References: <f1d765814f722fb2c99c9870b3cc2607b4eca2d7.camel@freebsd.org> <B9EFA4D4-C1AD-4181-B421-F6BD53434FA5@dons.net.au> <bfd784f6ac9c939dbe6a243336bc3b6eab02d4f5.camel@freebsd.org> <61B1AAF3-40F6-47BC-8F05-7491C13BF288@dons.net.au> <9E142F1A-5E8C-4410-91F5-7C80B3D0A15B@dons.net.au> <9D2ACA87-C2DB-40D9-9638-B0E215A4EEC0@dons.net.au> <0A7796DA-508B-4FE6-B5C0-391EC5F46C86@dons.net.au> <20190908134205.GO2559@kib.kiev.ua> <25BF53F1-23CF-4619-AB13-110566D6DC82@dons.net.au>
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On Mon, Sep 09, 2019 at 05:20:25PM +0930, O'Connor, Daniel wrote: > > > > On 8 Sep 2019, at 23:12, Konstantin Belousov <kostikbel@gmail.com> wrote: > >> I suppose it would be good to change it to the same structure as the feed forward clock stuff, that way it is much easier to change the number of hands at compile time.. > >> > > > > The reason to not increase it by default is the same as the reason why it > > was reduced. But since I did still not provided the analysis why increasing > > timehands count helps for Ian' and your case, I think that making it easy > > to increase the timehands number is due. > > I am a bit worried (based on your commit log for r303383) that the code now relies on it being 2 for correct function, although given I increased it to 10 and this system works fine perhaps not :) > It means that the sliding window where consumer should reach the writer to read the current timehands is larger. I think that in reality the cases where the latency of get*time*(9) KPI increased are very rare. Still the question is why your system have the negative impact from reducing the number of timehands. Interrupt should never interrupt tc_windup() because it is protected by spinlock. Silly question, are spinlocks functional on this machine ? > > Please see D21563 'Make timehands count selectable at boottime.' > > Looks good to me, I've installed it on the Beaglebone and it seems to be running OK so far. > > -- > Daniel O'Connor > "The nice thing about standards is that there > are so many of them to choose from." > -- Andrew Tanenbaum > >
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