From: Peter Hilber <peter.hilber@opensynergy.com> To: David Woodhouse <dwmw2@infradead.org>, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, virtio-dev@lists.oasis-open.org, linux-arm-kernel@lists.infradead.org, linux-rtc@vger.kernel.org, "virtio-comment@lists.oasis-open.org" <virtio-comment@lists.oasis-open.org> Cc: "Christopher S. Hall" <christopher.s.hall@intel.com>, Jason Wang <jasowang@redhat.com>, John Stultz <jstultz@google.com>, "Michael S. Tsirkin" <mst@redhat.com>, netdev@vger.kernel.org, Richard Cochran <richardcochran@gmail.com>, Stephen Boyd <sboyd@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Xuan Zhuo <xuanzhuo@linux.alibaba.com>, Marc Zyngier <maz@kernel.org>, Mark Rutland <mark.rutland@arm.com>, Daniel Lezcano <daniel.lezcano@linaro.org>, Alessandro Zummo <a.zummo@towertech.it>, Alexandre Belloni <alexandre.belloni@bootlin.com>, "Ridoux, Julien" <ridouxj@amazon.com>, Cornelia Huck <cohuck@redhat.com>, Parav Pandit <parav@nvidia.com> Subject: Re: [RFC PATCH v3 0/7] Add virtio_rtc module and related changes Date: Tue, 19 Mar 2024 14:47:26 +0100 [thread overview] Message-ID: <61364452-bdf5-4bd8-adb1-a9e6236c9d26@opensynergy.com> (raw) In-Reply-To: <9455F710-E38C-45DA-9883-EC034495ADEF@infradead.org> While the virtio-comment list is not available, now also CC'ing Parav, which may be interested in this virtio-rtc spec related discussion thread. On 14.03.24 15:19, David Woodhouse wrote: > On 14 March 2024 11:13:37 CET, Peter Hilber <peter.hilber@opensynergy.com> wrote: >>> To a certain extent, as long as the virtio-rtc device is designed to expose time precisely and unambiguously, it's less important if the Linux kernel *today* can use that. Although of course we should strive for that. Let's be...well, *unambiguous*, I suppose... that we've changed topics to discuss that though. >>> >> >> As Virtio is extensible (unlike hardware), my approach is to mostly specify >> only what also has a PoC user and a use case. > > If we get memory-mapped (X, Y, Z, ±x, ±y) I'll have a user and a use case on day one. Otherwise, as I said in my first response, I can go do that as a separate device and decide that virtio_rtc doesn't meet our needs (especially for maintaining accuracy over LM). We plan to add - leap second indication, - UTC-to-TAI offset, - clock smearing indication (including the noon-to-noon linear smearing variant which seems to be somewhat popular), and - clock accuracy indication to the initial spec and to the PoC implementation. However, due to resource restrictions, we cannot ourselves add the memory-mapped clock to the initial spec. Everyone is very welcome to contribute the memory-mapped clock to the spec, and I think it might then still make it to the initial version. > > My main concern for virto_rtc is that we avoid *ambiguity*. Yes, I get that it's extensible but we don't want a v1.0 of the spec, implemented by various hypervisors, which still leaves guests not knowing what the actual time is. That would not be good. And even UTC without a leap second indicator has that problem. Agreed. That should be addressed by the above changes. Best regards, Peter
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From: Peter Hilber <peter.hilber@opensynergy.com> To: David Woodhouse <dwmw2@infradead.org>, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, virtio-dev@lists.oasis-open.org, linux-arm-kernel@lists.infradead.org, linux-rtc@vger.kernel.org, "virtio-comment@lists.oasis-open.org" <virtio-comment@lists.oasis-open.org> Cc: "Christopher S. Hall" <christopher.s.hall@intel.com>, Jason Wang <jasowang@redhat.com>, John Stultz <jstultz@google.com>, "Michael S. Tsirkin" <mst@redhat.com>, netdev@vger.kernel.org, Richard Cochran <richardcochran@gmail.com>, Stephen Boyd <sboyd@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Xuan Zhuo <xuanzhuo@linux.alibaba.com>, Marc Zyngier <maz@kernel.org>, Mark Rutland <mark.rutland@arm.com>, Daniel Lezcano <daniel.lezcano@linaro.org>, Alessandro Zummo <a.zummo@towertech.it>, Alexandre Belloni <alexandre.belloni@bootlin.com>, "Ridoux, Julien" <ridouxj@amazon.com>, Cornelia Huck <cohuck@redhat.com>, Parav Pandit <parav@nvidia.com> Subject: Re: [RFC PATCH v3 0/7] Add virtio_rtc module and related changes Date: Tue, 19 Mar 2024 14:47:26 +0100 [thread overview] Message-ID: <61364452-bdf5-4bd8-adb1-a9e6236c9d26@opensynergy.com> (raw) In-Reply-To: <9455F710-E38C-45DA-9883-EC034495ADEF@infradead.org> While the virtio-comment list is not available, now also CC'ing Parav, which may be interested in this virtio-rtc spec related discussion thread. On 14.03.24 15:19, David Woodhouse wrote: > On 14 March 2024 11:13:37 CET, Peter Hilber <peter.hilber@opensynergy.com> wrote: >>> To a certain extent, as long as the virtio-rtc device is designed to expose time precisely and unambiguously, it's less important if the Linux kernel *today* can use that. Although of course we should strive for that. Let's be...well, *unambiguous*, I suppose... that we've changed topics to discuss that though. >>> >> >> As Virtio is extensible (unlike hardware), my approach is to mostly specify >> only what also has a PoC user and a use case. > > If we get memory-mapped (X, Y, Z, ±x, ±y) I'll have a user and a use case on day one. Otherwise, as I said in my first response, I can go do that as a separate device and decide that virtio_rtc doesn't meet our needs (especially for maintaining accuracy over LM). We plan to add - leap second indication, - UTC-to-TAI offset, - clock smearing indication (including the noon-to-noon linear smearing variant which seems to be somewhat popular), and - clock accuracy indication to the initial spec and to the PoC implementation. However, due to resource restrictions, we cannot ourselves add the memory-mapped clock to the initial spec. Everyone is very welcome to contribute the memory-mapped clock to the spec, and I think it might then still make it to the initial version. > > My main concern for virto_rtc is that we avoid *ambiguity*. Yes, I get that it's extensible but we don't want a v1.0 of the spec, implemented by various hypervisors, which still leaves guests not knowing what the actual time is. That would not be good. And even UTC without a leap second indicator has that problem. Agreed. That should be addressed by the above changes. Best regards, Peter _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2024-03-19 13:47 UTC|newest] Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-12-18 7:38 [virtio-dev] [RFC PATCH v3 0/7] Add virtio_rtc module and related changes Peter Hilber 2023-12-18 7:38 ` Peter Hilber 2023-12-18 7:38 ` Peter Hilber 2023-12-18 7:38 ` [RFC PATCH v3 1/7] timekeeping: Fix cross-timestamp interpolation on counter wrap Peter Hilber 2024-02-19 16:35 ` [tip: timers/core] " tip-bot2 for Peter Hilber 2023-12-18 7:38 ` [RFC PATCH v3 2/7] timekeeping: Fix cross-timestamp interpolation corner case decision Peter Hilber 2024-02-19 16:35 ` [tip: timers/core] " tip-bot2 for Peter Hilber 2023-12-18 7:38 ` [RFC PATCH v3 3/7] timekeeping: Fix cross-timestamp interpolation for non-x86 Peter Hilber 2024-02-19 16:35 ` [tip: timers/core] " tip-bot2 for Peter Hilber 2023-12-18 7:38 ` [virtio-dev] [RFC PATCH v3 4/7] virtio_rtc: Add module and driver core Peter Hilber 2023-12-18 7:38 ` Peter Hilber 2023-12-18 7:38 ` Peter Hilber 2023-12-18 7:38 ` [virtio-dev] [RFC PATCH v3 5/7] virtio_rtc: Add PTP clocks Peter Hilber 2023-12-18 7:38 ` Peter Hilber 2023-12-18 7:38 ` Peter Hilber 2023-12-18 7:38 ` [virtio-dev] [RFC PATCH v3 6/7] virtio_rtc: Add Arm Generic Timer cross-timestamping Peter Hilber 2023-12-18 7:38 ` Peter Hilber 2023-12-18 7:38 ` Peter Hilber 2023-12-18 7:38 ` [virtio-dev] [RFC PATCH v3 7/7] virtio_rtc: Add RTC class driver Peter Hilber 2023-12-18 7:38 ` Peter Hilber 2024-03-08 17:03 ` Alexandre Belloni 2024-03-11 18:28 ` Peter Hilber 2024-03-11 19:46 ` Alexandre Belloni 2024-03-13 9:13 ` Peter Hilber 2024-03-07 14:02 ` [RFC PATCH v3 0/7] Add virtio_rtc module and related changes David Woodhouse 2024-03-07 14:02 ` David Woodhouse 2024-03-08 10:32 ` Peter Hilber 2024-03-08 10:32 ` Peter Hilber 2024-03-08 12:33 ` David Woodhouse 2024-03-08 12:33 ` David Woodhouse 2024-03-11 18:24 ` Peter Hilber 2024-03-11 18:24 ` Peter Hilber 2024-03-12 17:15 ` David Woodhouse 2024-03-12 17:15 ` David Woodhouse 2024-03-13 9:45 ` Peter Hilber 2024-03-13 9:45 ` Peter Hilber 2024-03-13 11:18 ` Alexandre Belloni 2024-03-13 11:18 ` Alexandre Belloni 2024-03-13 12:29 ` David Woodhouse 2024-03-13 12:29 ` David Woodhouse 2024-03-13 12:58 ` Alexandre Belloni 2024-03-13 12:58 ` Alexandre Belloni 2024-03-13 14:06 ` David Woodhouse 2024-03-13 14:06 ` David Woodhouse 2024-03-13 14:50 ` Alexandre Belloni 2024-03-13 14:50 ` Alexandre Belloni 2024-03-13 20:12 ` Andrew Lunn 2024-03-13 20:12 ` Andrew Lunn 2024-03-14 9:13 ` Peter Hilber 2024-03-14 9:13 ` Peter Hilber 2024-03-13 17:50 ` Peter Hilber 2024-03-13 17:50 ` Peter Hilber 2024-03-13 14:15 ` Peter Hilber 2024-03-13 14:15 ` Peter Hilber 2024-03-13 12:45 ` David Woodhouse 2024-03-13 12:45 ` David Woodhouse 2024-03-13 17:50 ` Peter Hilber 2024-03-13 17:50 ` Peter Hilber 2024-03-13 18:18 ` David Woodhouse 2024-03-13 18:18 ` David Woodhouse 2024-03-14 10:13 ` Peter Hilber 2024-03-14 10:13 ` Peter Hilber 2024-03-14 14:19 ` David Woodhouse 2024-03-14 14:19 ` David Woodhouse 2024-03-19 13:47 ` Peter Hilber [this message] 2024-03-19 13:47 ` Peter Hilber 2024-03-20 17:22 ` David Woodhouse 2024-03-20 17:22 ` David Woodhouse
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