From mboxrd@z Thu Jan 1 00:00:00 1970 From: avagin@virtuozzo.com (Andrey Vagin) Date: Mon, 1 Oct 2018 23:20:47 +0000 Subject: [RFC 00/20] ns: Introduce Time Namespace In-Reply-To: References: <20180919205037.9574-1-dima@arista.com> <874lej6nny.fsf@xmission.com> <20180924205119.GA14833@outlook.office365.com> <874leezh8n.fsf@xmission.com> <20180925014150.GA6302@outlook.office365.com> <87zhw4rwiq.fsf@xmission.com> Message-ID: <20181001232033.GA31324@outlook.office365.com> Content-Type: text/plain; charset="UTF-8" Message-ID: <20181001232047.z9SZ22Ybrn0uP3c2W8ToF-xSpVP_SN2g1InJ5nn48MY@z> On Thu, Sep 27, 2018@11:41:49PM +0200, Thomas Gleixner wrote: > On Thu, 27 Sep 2018, Thomas Gleixner wrote: > > Add time skew via NTP/PTP into the picture and you might have to adjust > > timers as well, because you need to guarantee that they are not expiring > > early. > > > > I haven't looked through Dimitry's patches yet, but I don't see how this > > can work at all without introducing subtle issues all over the place. > > And just a quick scan tells me that this is broken. Timers will expire > early or late. The latter is acceptible to some extent, but larger delays > might come with surprise. Expiring early is an absolute nono. Do you mean that we have to adjust all timers after changing offset for CLOCK_MONOTONIC or CLOCK_BOOTTIME? Our idea is that offsets for monotonic and boot times will be set immediately after creating a time namespace before using any timers. It is interesting to think what a use-case for changing these offsets after creating timers. It may be useful for testing needs. A user sets a timer in an hour and then change a clock offset forward and check that a test application handles the timer properly. > > Thanks, > > tglx >