linux/drivers/ptp/Kconfig

255 lines
8.4 KiB

ethernet: fix PTP_1588_CLOCK dependencies The 'imply' keyword does not do what most people think it does, it only politely asks Kconfig to turn on another symbol, but does not prevent it from being disabled manually or built as a loadable module when the user is built-in. In the ICE driver, the latter now causes a link failure: aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function `ice_eth_ioctl': ice_main.c:(.text+0x13b0): undefined reference to `ice_ptp_get_ts_config' ice_main.c:(.text+0x13b0): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `ice_ptp_get_ts_config' aarch64-linux-ld: ice_main.c:(.text+0x13bc): undefined reference to `ice_ptp_set_ts_config' ice_main.c:(.text+0x13bc): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `ice_ptp_set_ts_config' aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function `ice_prepare_for_reset': ice_main.c:(.text+0x31fc): undefined reference to `ice_ptp_release' ice_main.c:(.text+0x31fc): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `ice_ptp_release' aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function `ice_rebuild': This is a recurring problem in many drivers, and we have discussed it several times befores, without reaching a consensus. I'm providing a link to the previous email thread for reference, which discusses some related problems. To solve the dependency issue better than the 'imply' keyword, introduce a separate Kconfig symbol "CONFIG_PTP_1588_CLOCK_OPTIONAL" that any driver can depend on if it is able to use PTP support when available, but works fine without it. Whenever CONFIG_PTP_1588_CLOCK=m, those drivers are then prevented from being built-in, the same way as with a 'depends on PTP_1588_CLOCK || !PTP_1588_CLOCK' dependency that does the same trick, but that can be rather confusing when you first see it. Since this should cover the dependencies correctly, the IS_REACHABLE() hack in the header is no longer needed now, and can be turned back into a normal IS_ENABLED() check. Any driver that gets the dependency wrong will now cause a link time failure rather than being unable to use PTP support when that is in a loadable module. However, the two recently added ptp_get_vclocks_index() and ptp_convert_timestamp() interfaces are only called from builtin code with ethtool and socket timestamps, so keep the current behavior by stubbing those out completely when PTP is in a loadable module. This should be addressed properly in a follow-up. As Richard suggested, we may want to actually turn PTP support into a 'bool' option later on, preventing it from being a loadable module altogether, which would be one way to solve the problem with the ethtool interface. Fixes: 06c16d89d2cb ("ice: register 1588 PTP clock device object for E810 devices") Link: https://lore.kernel.org/netdev/20210804121318.337276-1-arnd@kernel.org/ Link: https://lore.kernel.org/netdev/CAK8P3a06enZOf=XyZ+zcAwBczv41UuCTz+=0FMf2gBz1_cOnZQ@mail.gmail.com/ Link: https://lore.kernel.org/netdev/CAK8P3a3=eOxE-K25754+fB_-i_0BZzf9a9RfPTX3ppSwu9WZXw@mail.gmail.com/ Link: https://lore.kernel.org/netdev/20210726084540.3282344-1-arnd@kernel.org/ Acked-by: Shannon Nelson <snelson@pensando.io> Acked-by: Jacob Keller <jacob.e.keller@intel.com> Acked-by: Richard Cochran <richardcochran@gmail.com> Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by: Arnd Bergmann <arnd@arndb.de> Link: https://lore.kernel.org/r/20210812183509.1362782-1-arnd@kernel.org Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2021-08-12 20:33:58 +02:00
net: ptp: move PTP classifier in its own file This commit fixes a build error reported by Fengguang, that is triggered when CONFIG_NETWORK_PHY_TIMESTAMPING is not set: ERROR: "ptp_classify_raw" [drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe.ko] undefined! The fix is to introduce its own file for the PTP BPF classifier, so that PTP_1588_CLOCK and/or NETWORK_PHY_TIMESTAMPING can select it independently from each other. IXP4xx driver on ARM needs to select it as well since it does not seem to select PTP_1588_CLOCK or similar that would pull it in automatically. This also allows for hiding all of the internals of the BPF PTP program inside that file, and only exporting relevant API bits to drivers. This patch also adds a kdoc documentation of ptp_classify_raw() API to make it clear that it can return PTP_CLASS_* defines. Also, the BPF program has been translated into bpf_asm code, so that it can be more easily read and altered (extensively documented in [1]). In the kernel tree under tools/net/ we have bpf_asm and bpf_dbg tools, so the commented program can simply be translated via `./bpf_asm -c prog` where prog is a file that contains the commented code. This makes it easily readable/verifiable and when there's a need to change something, jump offsets etc do not need to be replaced manually which can be very error prone. Instead, a newly translated version via bpf_asm can simply replace the old code. I have checked opcode diffs before/after and it's the very same filter. [1] Documentation/networking/filter.txt Fixes: 164d8c666521 ("net: ptp: do not reimplement PTP/BPF classifier") Reported-by: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Cc: Richard Cochran <richardcochran@gmail.com> Cc: Jiri Benc <jbenc@redhat.com> Acked-by: Richard Cochran <richardcochran@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-04-01 16:20:23 +02:00
ethernet: fix PTP_1588_CLOCK dependencies The 'imply' keyword does not do what most people think it does, it only politely asks Kconfig to turn on another symbol, but does not prevent it from being disabled manually or built as a loadable module when the user is built-in. In the ICE driver, the latter now causes a link failure: aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function `ice_eth_ioctl': ice_main.c:(.text+0x13b0): undefined reference to `ice_ptp_get_ts_config' ice_main.c:(.text+0x13b0): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `ice_ptp_get_ts_config' aarch64-linux-ld: ice_main.c:(.text+0x13bc): undefined reference to `ice_ptp_set_ts_config' ice_main.c:(.text+0x13bc): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `ice_ptp_set_ts_config' aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function `ice_prepare_for_reset': ice_main.c:(.text+0x31fc): undefined reference to `ice_ptp_release' ice_main.c:(.text+0x31fc): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `ice_ptp_release' aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function `ice_rebuild': This is a recurring problem in many drivers, and we have discussed it several times befores, without reaching a consensus. I'm providing a link to the previous email thread for reference, which discusses some related problems. To solve the dependency issue better than the 'imply' keyword, introduce a separate Kconfig symbol "CONFIG_PTP_1588_CLOCK_OPTIONAL" that any driver can depend on if it is able to use PTP support when available, but works fine without it. Whenever CONFIG_PTP_1588_CLOCK=m, those drivers are then prevented from being built-in, the same way as with a 'depends on PTP_1588_CLOCK || !PTP_1588_CLOCK' dependency that does the same trick, but that can be rather confusing when you first see it. Since this should cover the dependencies correctly, the IS_REACHABLE() hack in the header is no longer needed now, and can be turned back into a normal IS_ENABLED() check. Any driver that gets the dependency wrong will now cause a link time failure rather than being unable to use PTP support when that is in a loadable module. However, the two recently added ptp_get_vclocks_index() and ptp_convert_timestamp() interfaces are only called from builtin code with ethtool and socket timestamps, so keep the current behavior by stubbing those out completely when PTP is in a loadable module. This should be addressed properly in a follow-up. As Richard suggested, we may want to actually turn PTP support into a 'bool' option later on, preventing it from being a loadable module altogether, which would be one way to solve the problem with the ethtool interface. Fixes: 06c16d89d2cb ("ice: register 1588 PTP clock device object for E810 devices") Link: https://lore.kernel.org/netdev/20210804121318.337276-1-arnd@kernel.org/ Link: https://lore.kernel.org/netdev/CAK8P3a06enZOf=XyZ+zcAwBczv41UuCTz+=0FMf2gBz1_cOnZQ@mail.gmail.com/ Link: https://lore.kernel.org/netdev/CAK8P3a3=eOxE-K25754+fB_-i_0BZzf9a9RfPTX3ppSwu9WZXw@mail.gmail.com/ Link: https://lore.kernel.org/netdev/20210726084540.3282344-1-arnd@kernel.org/ Acked-by: Shannon Nelson <snelson@pensando.io> Acked-by: Jacob Keller <jacob.e.keller@intel.com> Acked-by: Richard Cochran <richardcochran@gmail.com> Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by: Arnd Bergmann <arnd@arndb.de> Link: https://lore.kernel.org/r/20210812183509.1362782-1-arnd@kernel.org Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2021-08-12 20:33:58 +02:00
ptp_clock: Allow for it to be optional In order to break the hard dependency between the PTP clock subsystem and ethernet drivers capable of being clock providers, this patch provides simple PTP stub functions to allow linkage of those drivers into the kernel even when the PTP subsystem is configured out. Drivers must be ready to accept NULL from ptp_clock_register() in that case. And to make it possible for PTP to be configured out, the select statement in those driver's Kconfig menu entries is converted to the new "imply" statement. This way the PTP subsystem may have Kconfig dependencies of its own, such as POSIX_TIMERS, without having to make those ethernet drivers unavailable if POSIX timers are cconfigured out. And when support for POSIX timers is selected again then the default config option for PTP clock support will automatically be adjusted accordingly. The pch_gbe driver is a bit special as it relies on extra code in drivers/ptp/ptp_pch.c. Therefore we let the make process descend into drivers/ptp/ even if PTP_1588_CLOCK is unselected. Signed-off-by: Nicolas Pitre <nico@linaro.org> Acked-by: Richard Cochran <richardcochran@gmail.com> Acked-by: Edward Cree <ecree@solarflare.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: John Stultz <john.stultz@linaro.org> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Cc: Paul Bolle <pebolle@tiscali.nl> Cc: linux-kbuild@vger.kernel.org Cc: netdev@vger.kernel.org Cc: Michal Marek <mmarek@suse.com> Link: http://lkml.kernel.org/r/1478841010-28605-4-git-send-email-nicolas.pitre@linaro.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2016-11-11 00:10:07 -05:00
ptp_clock: Allow for it to be optional In order to break the hard dependency between the PTP clock subsystem and ethernet drivers capable of being clock providers, this patch provides simple PTP stub functions to allow linkage of those drivers into the kernel even when the PTP subsystem is configured out. Drivers must be ready to accept NULL from ptp_clock_register() in that case. And to make it possible for PTP to be configured out, the select statement in those driver's Kconfig menu entries is converted to the new "imply" statement. This way the PTP subsystem may have Kconfig dependencies of its own, such as POSIX_TIMERS, without having to make those ethernet drivers unavailable if POSIX timers are cconfigured out. And when support for POSIX timers is selected again then the default config option for PTP clock support will automatically be adjusted accordingly. The pch_gbe driver is a bit special as it relies on extra code in drivers/ptp/ptp_pch.c. Therefore we let the make process descend into drivers/ptp/ even if PTP_1588_CLOCK is unselected. Signed-off-by: Nicolas Pitre <nico@linaro.org> Acked-by: Richard Cochran <richardcochran@gmail.com> Acked-by: Edward Cree <ecree@solarflare.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: John Stultz <john.stultz@linaro.org> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Cc: Paul Bolle <pebolle@tiscali.nl> Cc: linux-kbuild@vger.kernel.org Cc: netdev@vger.kernel.org Cc: Michal Marek <mmarek@suse.com> Link: http://lkml.kernel.org/r/1478841010-28605-4-git-send-email-nicolas.pitre@linaro.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2016-11-11 00:10:07 -05:00
ethernet: fix PTP_1588_CLOCK dependencies The 'imply' keyword does not do what most people think it does, it only politely asks Kconfig to turn on another symbol, but does not prevent it from being disabled manually or built as a loadable module when the user is built-in. In the ICE driver, the latter now causes a link failure: aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function `ice_eth_ioctl': ice_main.c:(.text+0x13b0): undefined reference to `ice_ptp_get_ts_config' ice_main.c:(.text+0x13b0): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `ice_ptp_get_ts_config' aarch64-linux-ld: ice_main.c:(.text+0x13bc): undefined reference to `ice_ptp_set_ts_config' ice_main.c:(.text+0x13bc): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `ice_ptp_set_ts_config' aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function `ice_prepare_for_reset': ice_main.c:(.text+0x31fc): undefined reference to `ice_ptp_release' ice_main.c:(.text+0x31fc): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `ice_ptp_release' aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function `ice_rebuild': This is a recurring problem in many drivers, and we have discussed it several times befores, without reaching a consensus. I'm providing a link to the previous email thread for reference, which discusses some related problems. To solve the dependency issue better than the 'imply' keyword, introduce a separate Kconfig symbol "CONFIG_PTP_1588_CLOCK_OPTIONAL" that any driver can depend on if it is able to use PTP support when available, but works fine without it. Whenever CONFIG_PTP_1588_CLOCK=m, those drivers are then prevented from being built-in, the same way as with a 'depends on PTP_1588_CLOCK || !PTP_1588_CLOCK' dependency that does the same trick, but that can be rather confusing when you first see it. Since this should cover the dependencies correctly, the IS_REACHABLE() hack in the header is no longer needed now, and can be turned back into a normal IS_ENABLED() check. Any driver that gets the dependency wrong will now cause a link time failure rather than being unable to use PTP support when that is in a loadable module. However, the two recently added ptp_get_vclocks_index() and ptp_convert_timestamp() interfaces are only called from builtin code with ethtool and socket timestamps, so keep the current behavior by stubbing those out completely when PTP is in a loadable module. This should be addressed properly in a follow-up. As Richard suggested, we may want to actually turn PTP support into a 'bool' option later on, preventing it from being a loadable module altogether, which would be one way to solve the problem with the ethtool interface. Fixes: 06c16d89d2cb ("ice: register 1588 PTP clock device object for E810 devices") Link: https://lore.kernel.org/netdev/20210804121318.337276-1-arnd@kernel.org/ Link: https://lore.kernel.org/netdev/CAK8P3a06enZOf=XyZ+zcAwBczv41UuCTz+=0FMf2gBz1_cOnZQ@mail.gmail.com/ Link: https://lore.kernel.org/netdev/CAK8P3a3=eOxE-K25754+fB_-i_0BZzf9a9RfPTX3ppSwu9WZXw@mail.gmail.com/ Link: https://lore.kernel.org/netdev/20210726084540.3282344-1-arnd@kernel.org/ Acked-by: Shannon Nelson <snelson@pensando.io> Acked-by: Jacob Keller <jacob.e.keller@intel.com> Acked-by: Richard Cochran <richardcochran@gmail.com> Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by: Arnd Bergmann <arnd@arndb.de> Link: https://lore.kernel.org/r/20210812183509.1362782-1-arnd@kernel.org Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2021-08-12 20:33:58 +02:00
ptp: arm/arm64: Enable ptp_kvm for arm/arm64 Currently, there is no mechanism to keep time sync between guest and host in arm/arm64 virtualization environment. Time in guest will drift compared with host after boot up as they may both use third party time sources to correct their time respectively. The time deviation will be in order of milliseconds. But in some scenarios,like in cloud environment, we ask for higher time precision. kvm ptp clock, which chooses the host clock source as a reference clock to sync time between guest and host, has been adopted by x86 which takes the time sync order from milliseconds to nanoseconds. This patch enables kvm ptp clock for arm/arm64 and improves clock sync precision significantly. Test result comparisons between with kvm ptp clock and without it in arm/arm64 are as follows. This test derived from the result of command 'chronyc sources'. we should take more care of the last sample column which shows the offset between the local clock and the source at the last measurement. no kvm ptp in guest: MS Name/IP address Stratum Poll Reach LastRx Last sample ======================================================================== ^* dns1.synet.edu.cn 2 6 377 13 +1040us[+1581us] +/- 21ms ^* dns1.synet.edu.cn 2 6 377 21 +1040us[+1581us] +/- 21ms ^* dns1.synet.edu.cn 2 6 377 29 +1040us[+1581us] +/- 21ms ^* dns1.synet.edu.cn 2 6 377 37 +1040us[+1581us] +/- 21ms ^* dns1.synet.edu.cn 2 6 377 45 +1040us[+1581us] +/- 21ms ^* dns1.synet.edu.cn 2 6 377 53 +1040us[+1581us] +/- 21ms ^* dns1.synet.edu.cn 2 6 377 61 +1040us[+1581us] +/- 21ms ^* dns1.synet.edu.cn 2 6 377 4 -130us[ +796us] +/- 21ms ^* dns1.synet.edu.cn 2 6 377 12 -130us[ +796us] +/- 21ms ^* dns1.synet.edu.cn 2 6 377 20 -130us[ +796us] +/- 21ms in host: MS Name/IP address Stratum Poll Reach LastRx Last sample ======================================================================== ^* 120.25.115.20 2 7 377 72 -470us[ -603us] +/- 18ms ^* 120.25.115.20 2 7 377 92 -470us[ -603us] +/- 18ms ^* 120.25.115.20 2 7 377 112 -470us[ -603us] +/- 18ms ^* 120.25.115.20 2 7 377 2 +872ns[-6808ns] +/- 17ms ^* 120.25.115.20 2 7 377 22 +872ns[-6808ns] +/- 17ms ^* 120.25.115.20 2 7 377 43 +872ns[-6808ns] +/- 17ms ^* 120.25.115.20 2 7 377 63 +872ns[-6808ns] +/- 17ms ^* 120.25.115.20 2 7 377 83 +872ns[-6808ns] +/- 17ms ^* 120.25.115.20 2 7 377 103 +872ns[-6808ns] +/- 17ms ^* 120.25.115.20 2 7 377 123 +872ns[-6808ns] +/- 17ms The dns1.synet.edu.cn is the network reference clock for guest and 120.25.115.20 is the network reference clock for host. we can't get the clock error between guest and host directly, but a roughly estimated value will be in order of hundreds of us to ms. with kvm ptp in guest: chrony has been disabled in host to remove the disturb by network clock. MS Name/IP address Stratum Poll Reach LastRx Last sample ======================================================================== * PHC0 0 3 377 8 -7ns[ +1ns] +/- 3ns * PHC0 0 3 377 8 +1ns[ +16ns] +/- 3ns * PHC0 0 3 377 6 -4ns[ -0ns] +/- 6ns * PHC0 0 3 377 6 -8ns[ -12ns] +/- 5ns * PHC0 0 3 377 5 +2ns[ +4ns] +/- 4ns * PHC0 0 3 377 13 +2ns[ +4ns] +/- 4ns * PHC0 0 3 377 12 -4ns[ -6ns] +/- 4ns * PHC0 0 3 377 11 -8ns[ -11ns] +/- 6ns * PHC0 0 3 377 10 -14ns[ -20ns] +/- 4ns * PHC0 0 3 377 8 +4ns[ +5ns] +/- 4ns The PHC0 is the ptp clock which choose the host clock as its source clock. So we can see that the clock difference between host and guest is in order of ns. Cc: Mark Rutland <mark.rutland@arm.com> Acked-by: Richard Cochran <richardcochran@gmail.com> Signed-off-by: Jianyong Wu <jianyong.wu@arm.com> Signed-off-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20201209060932.212364-8-jianyong.wu@arm.com
2020-12-09 14:09:30 +08:00
ptp: Add support for the AMZNC10C 'vmclock' device The vmclock device addresses the problem of live migration with precision clocks. The tolerances of a hardware counter (e.g. TSC) are typically around ±50PPM. A guest will use NTP/PTP/PPS to discipline that counter against an external source of 'real' time, and track the precise frequency of the counter as it changes with environmental conditions. When a guest is live migrated, anything it knows about the frequency of the underlying counter becomes invalid. It may move from a host where the counter running at -50PPM of its nominal frequency, to a host where it runs at +50PPM. There will also be a step change in the value of the counter, as the correctness of its absolute value at migration is limited by the accuracy of the source and destination host's time synchronization. In its simplest form, the device merely advertises a 'disruption_marker' which indicates that the guest should throw away any NTP synchronization it thinks it has, and start again. Because the shared memory region can be exposed all the way to userspace through the /dev/vmclock0 node, applications can still use time from a fast vDSO 'system call', and check the disruption marker to be sure that their timestamp is indeed truthful. The structure also allows for the precise time, as known by the host, to be exposed directly to guests so that they don't have to wait for NTP to resync from scratch. The PTP driver consumes this information if present. Like the KVM PTP clock, this PTP driver can convert TSC-based cross timestamps into KVM clock values. Unlike the KVM PTP clock, it does so only when such is actually helpful. The values and fields are based on the nascent virtio-rtc specification, and the intent is that a version (hopefully precisely this version) of this structure will be included as an optional part of that spec. In the meantime, this driver supports the simple ACPI form of the device which is being shipped in certain commercial hypervisors (and submitted for inclusion in QEMU). Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> Acked-by: Richard Cochran <richardcochran@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2024-10-06 08:17:58 +01:00
ptp: Add support for the AMZNC10C 'vmclock' device The vmclock device addresses the problem of live migration with precision clocks. The tolerances of a hardware counter (e.g. TSC) are typically around ±50PPM. A guest will use NTP/PTP/PPS to discipline that counter against an external source of 'real' time, and track the precise frequency of the counter as it changes with environmental conditions. When a guest is live migrated, anything it knows about the frequency of the underlying counter becomes invalid. It may move from a host where the counter running at -50PPM of its nominal frequency, to a host where it runs at +50PPM. There will also be a step change in the value of the counter, as the correctness of its absolute value at migration is limited by the accuracy of the source and destination host's time synchronization. In its simplest form, the device merely advertises a 'disruption_marker' which indicates that the guest should throw away any NTP synchronization it thinks it has, and start again. Because the shared memory region can be exposed all the way to userspace through the /dev/vmclock0 node, applications can still use time from a fast vDSO 'system call', and check the disruption marker to be sure that their timestamp is indeed truthful. The structure also allows for the precise time, as known by the host, to be exposed directly to guests so that they don't have to wait for NTP to resync from scratch. The PTP driver consumes this information if present. Like the KVM PTP clock, this PTP driver can convert TSC-based cross timestamps into KVM clock values. Unlike the KVM PTP clock, it does so only when such is actually helpful. The values and fields are based on the nascent virtio-rtc specification, and the intent is that a version (hopefully precisely this version) of this structure will be included as an optional part of that spec. In the meantime, this driver supports the simple ACPI form of the device which is being shipped in certain commercial hypervisors (and submitted for inclusion in QEMU). Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> Acked-by: Richard Cochran <richardcochran@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2024-10-06 08:17:58 +01:00
ptp: Add support for the AMZNC10C 'vmclock' device The vmclock device addresses the problem of live migration with precision clocks. The tolerances of a hardware counter (e.g. TSC) are typically around ±50PPM. A guest will use NTP/PTP/PPS to discipline that counter against an external source of 'real' time, and track the precise frequency of the counter as it changes with environmental conditions. When a guest is live migrated, anything it knows about the frequency of the underlying counter becomes invalid. It may move from a host where the counter running at -50PPM of its nominal frequency, to a host where it runs at +50PPM. There will also be a step change in the value of the counter, as the correctness of its absolute value at migration is limited by the accuracy of the source and destination host's time synchronization. In its simplest form, the device merely advertises a 'disruption_marker' which indicates that the guest should throw away any NTP synchronization it thinks it has, and start again. Because the shared memory region can be exposed all the way to userspace through the /dev/vmclock0 node, applications can still use time from a fast vDSO 'system call', and check the disruption marker to be sure that their timestamp is indeed truthful. The structure also allows for the precise time, as known by the host, to be exposed directly to guests so that they don't have to wait for NTP to resync from scratch. The PTP driver consumes this information if present. Like the KVM PTP clock, this PTP driver can convert TSC-based cross timestamps into KVM clock values. Unlike the KVM PTP clock, it does so only when such is actually helpful. The values and fields are based on the nascent virtio-rtc specification, and the intent is that a version (hopefully precisely this version) of this structure will be included as an optional part of that spec. In the meantime, this driver supports the simple ACPI form of the device which is being shipped in certain commercial hypervisors (and submitted for inclusion in QEMU). Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> Acked-by: Richard Cochran <richardcochran@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2024-10-06 08:17:58 +01:00