Messages in this thread | | | Date | Mon, 07 Sep 2020 09:54:57 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64 |
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On 2020-09-07 09:40, Jianyong Wu wrote: > Hi Marc, > >> -----Original Message----- >> From: Marc Zyngier <maz@kernel.org> >> Sent: Saturday, September 5, 2020 7:02 PM >> To: Jianyong Wu <Jianyong.Wu@arm.com> >> Cc: netdev@vger.kernel.org; yangbo.lu@nxp.com; john.stultz@linaro.org; >> tglx@linutronix.de; pbonzini@redhat.com; >> sean.j.christopherson@intel.com; >> richardcochran@gmail.com; Mark Rutland <Mark.Rutland@arm.com>; >> will@kernel.org; Suzuki Poulose <Suzuki.Poulose@arm.com>; Steven Price >> <Steven.Price@arm.com>; linux-kernel@vger.kernel.org; linux-arm- >> kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu; >> kvm@vger.kernel.org; Steve Capper <Steve.Capper@arm.com>; Justin He >> <Justin.He@arm.com>; nd <nd@arm.com> >> Subject: Re: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64 >> >> On Fri, 04 Sep 2020 10:27:42 +0100, >> Jianyong Wu <jianyong.wu@arm.com> wrote: >> > >> > Currently, there is no mechanism to keep time sync between guest and >> > host in 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 >> > envirenment, we ask for higher time precision. >> > >> > kvm ptp clock, which choose the host clock source as a reference clock >> > to sync time between guest and host, has been adopted by x86 which >> > makes the time sync order from milliseconds to nanoseconds. >> > >> > This patch enables kvm ptp clock for arm64 and improve clock sync >> > precison significantly. >> > >> > Test result comparisons between with kvm ptp clock and without it in >> > 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. >> > >> > Signed-off-by: Jianyong Wu <jianyong.wu@arm.com> >> > --- >> > drivers/clocksource/arm_arch_timer.c | 24 +++++++++++++ >> > drivers/ptp/Kconfig | 2 +- >> > drivers/ptp/ptp_kvm_arm64.c | 53 >> ++++++++++++++++++++++++++++ >> > 3 files changed, 78 insertions(+), 1 deletion(-) create mode 100644 >> > drivers/ptp/ptp_kvm_arm64.c >> > >> > diff --git a/drivers/clocksource/arm_arch_timer.c >> > b/drivers/clocksource/arm_arch_timer.c >> > index d55acffb0b90..aaf286e90092 100644 >> > --- a/drivers/clocksource/arm_arch_timer.c >> > +++ b/drivers/clocksource/arm_arch_timer.c >> > @@ -1650,3 +1650,27 @@ static int __init arch_timer_acpi_init(struct >> > acpi_table_header *table) } TIMER_ACPI_DECLARE(arch_timer, >> > ACPI_SIG_GTDT, arch_timer_acpi_init); #endif >> > + >> > +#if IS_ENABLED(CONFIG_PTP_1588_CLOCK_KVM) >> > +#include <linux/arm-smccc.h> >> > +int kvm_arch_ptp_get_crosststamp(unsigned long *cycle, struct >> timespec64 *ts, >> > + struct clocksource **cs) >> > +{ >> > + struct arm_smccc_res hvc_res; >> > + ktime_t ktime; >> > + >> > + /* Currently, linux guest will always use the virtual counter */ >> > + >> arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FU >> NC_ID, >> > + ARM_PTP_VIRT_COUNTER, &hvc_res); >> > + if ((long long)(hvc_res.a0) < 0) >> > + return -EOPNOTSUPP; >> > + >> > + ktime = (long long)hvc_res.a0; >> > + *ts = ktime_to_timespec64(ktime); >> > + *cycle = (long long)hvc_res.a1; >> > + *cs = &clocksource_counter; >> > + >> > + return 0; >> > +} >> > +EXPORT_SYMBOL_GPL(kvm_arch_ptp_get_crosststamp); >> > +#endif >> > diff --git a/drivers/ptp/Kconfig b/drivers/ptp/Kconfig index >> > 942f72d8151d..127e96f14f89 100644 >> > --- a/drivers/ptp/Kconfig >> > +++ b/drivers/ptp/Kconfig >> > @@ -106,7 +106,7 @@ config PTP_1588_CLOCK_PCH config >> > PTP_1588_CLOCK_KVM >> > tristate "KVM virtual PTP clock" >> > depends on PTP_1588_CLOCK >> > - depends on KVM_GUEST && X86 >> > + depends on KVM_GUEST && X86 || ARM64 && ARM_ARCH_TIMER >> && >> > +ARM_PSCI_FW >> > default y >> > help >> > This driver adds support for using kvm infrastructure as a PTP >> > diff --git a/drivers/ptp/ptp_kvm_arm64.c b/drivers/ptp/ptp_kvm_arm64.c >> > new file mode 100644 index 000000000000..961abed93dfd >> > --- /dev/null >> > +++ b/drivers/ptp/ptp_kvm_arm64.c >> > @@ -0,0 +1,53 @@ >> > +// SPDX-License-Identifier: GPL-2.0-only >> > +/* >> > + * Virtual PTP 1588 clock for use with KVM guests >> > + * Copyright (C) 2019 ARM Ltd. >> > + * All Rights Reserved >> > + */ >> > + >> > +#include <linux/kernel.h> >> > +#include <linux/err.h> >> > +#include <asm/hypervisor.h> >> > +#include <linux/module.h> >> > +#include <linux/psci.h> >> > +#include <linux/arm-smccc.h> >> > +#include <linux/timecounter.h> >> > +#include <linux/sched/clock.h> >> > +#include <asm/arch_timer.h> >> > + >> > +int kvm_arch_ptp_init(void) >> > +{ >> > + struct arm_smccc_res hvc_res; >> > + >> > + >> arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_FEATUR >> ES_FUNC_ID, >> > + &hvc_res); >> > + if (!(hvc_res.a0 | BIT(ARM_SMCCC_KVM_FUNC_KVM_PTP))) >> > + return -EOPNOTSUPP; >> > + >> > + return 0; >> >> What happens if the >> ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID function isn't >> implemented (on an old kernel or a non-KVM hypervisor)? The expected >> behaviour is that a0 will contain SMCCC_RET_NOT_SUPPORTED, which is >> -1. >> The result is that this function always returns "supported". Not an >> acceptable >> behaviour. >> > Oh! it's really a stupid mistake, should be "&" not "|".
But even then. (-1 & whatever) is always true.
M. -- Jazz is not dead. It just smells funny...
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