From: John Stultz <john.stultz@linaro.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: David Vrabel <david.vrabel@citrix.com>,
xen-devel@lists.xen.org,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 2/4] time: add a notifier chain for when the system time is stepped
Date: Fri, 21 Jun 2013 09:22:46 -0700 [thread overview]
Message-ID: <51C47DD6.3000004@linaro.org> (raw)
In-Reply-To: <alpine.DEB.2.02.1306210953480.4013@ionos.tec.linutronix.de>
On 06/21/2013 12:57 AM, Thomas Gleixner wrote:
> On Thu, 20 Jun 2013, David Vrabel wrote:
>
>> From: David Vrabel <david.vrabel@citrix.com>
>>
>> The high resolution timer code gets notified of step changes to the
>> system time with clock_was_set() or clock_was_set_delayed() calls. If
>> other parts of the kernel require similar notification there is no
>> clear place to hook into.
> You fail to explain why any other part of the kernel requires a
> notification.
>
> We went great length to confine timekeeping inside the core code and
> now you add random notifiers along with totally ugly tasklet
> constructs. What for?
>
> Without a reasonable explanation of the problem you are trying to
> solve this is going nowhere near the tree.
It took awhile for me to get why it was needed as well.
My understanding is that on Xen, they want the hypervisor's virtual RTC
needs to be aligned with Dom0s system time (so that DomN guests boot
with the correct time). Thus changes to the system time need to cause
Dom0 to update the virtual RTC.
Its not terribly unlike the timerfd notification we do to userspace, but
instead is done for the Dom0 Xen management code.
I do agree we need to keep users of the notification on a short leash
(hopefully keeping the interface behind some sort of internal.h header
file) so its easy to see when folks start trying to use it.
thanks
-john
next prev parent reply other threads:[~2013-06-21 16:22 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-20 19:16 [PATCHv5 0/4] xen: maintain an accurate persistent clock in more cases David Vrabel
2013-06-20 19:16 ` [PATCH 1/4] hrtimers: provide a hrtimers_late_resume() call David Vrabel
2013-06-21 7:53 ` Thomas Gleixner
2013-06-21 12:32 ` David Vrabel
2013-06-21 14:32 ` Thomas Gleixner
2013-06-21 17:30 ` David Vrabel
2013-06-21 21:24 ` Thomas Gleixner
2013-06-20 19:16 ` [PATCH 2/4] time: add a notifier chain for when the system time is stepped David Vrabel
2013-06-21 7:57 ` Thomas Gleixner
2013-06-21 12:41 ` David Vrabel
2013-06-21 23:06 ` Thomas Gleixner
2013-06-24 10:51 ` David Vrabel
2013-06-24 16:30 ` Thomas Gleixner
2013-06-24 17:00 ` David Vrabel
2013-06-24 17:50 ` John Stultz
2013-06-24 19:55 ` Thomas Gleixner
2013-06-21 16:22 ` John Stultz [this message]
2013-06-20 19:16 ` [PATCH 3/4] x86/xen: sync the wallclock " David Vrabel
2013-06-20 19:16 ` [PATCH 4/4] x86/xen: sync the CMOS RTC as well as the Xen wallclock David Vrabel
2013-06-20 20:03 ` [PATCHv5 0/4] xen: maintain an accurate persistent clock in more cases John Stultz
2013-06-21 18:31 ` Konrad Rzeszutek Wilk
-- strict thread matches above, loose matches on Subject: below --
2013-06-19 15:25 [PATCHv4 " David Vrabel
2013-06-19 15:25 ` [PATCH 2/4] time: add a notifier chain for when the system time is stepped David Vrabel
2013-06-19 16:52 ` John Stultz
2013-06-19 17:13 ` Konrad Rzeszutek Wilk
2013-06-19 17:38 ` John Stultz
2013-06-20 10:50 ` David Vrabel
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