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Date: Mon, 7 Sep 2020 08:40:34 +0000 From: Jianyong Wu <Jianyong.Wu@....com> To: Marc Zyngier <maz@...nel.org> CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "yangbo.lu@....com" <yangbo.lu@....com>, "john.stultz@...aro.org" <john.stultz@...aro.org>, "tglx@...utronix.de" <tglx@...utronix.de>, "pbonzini@...hat.com" <pbonzini@...hat.com>, "sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>, "richardcochran@...il.com" <richardcochran@...il.com>, Mark Rutland <Mark.Rutland@....com>, "will@...nel.org" <will@...nel.org>, Suzuki Poulose <Suzuki.Poulose@....com>, Steven Price <Steven.Price@....com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, Steve Capper <Steve.Capper@....com>, Justin He <Justin.He@....com>, nd <nd@....com> Subject: RE: [PATCH v14 08/10] ptp: arm64: Enable ptp_kvm for arm64 Hi Marc, > -----Original Message----- > From: Marc Zyngier <maz@...nel.org> > Sent: Saturday, September 5, 2020 7:02 PM > To: Jianyong Wu <Jianyong.Wu@....com> > Cc: netdev@...r.kernel.org; yangbo.lu@....com; john.stultz@...aro.org; > tglx@...utronix.de; pbonzini@...hat.com; sean.j.christopherson@...el.com; > richardcochran@...il.com; Mark Rutland <Mark.Rutland@....com>; > will@...nel.org; Suzuki Poulose <Suzuki.Poulose@....com>; Steven Price > <Steven.Price@....com>; linux-kernel@...r.kernel.org; linux-arm- > kernel@...ts.infradead.org; kvmarm@...ts.cs.columbia.edu; > kvm@...r.kernel.org; Steve Capper <Steve.Capper@....com>; Justin He > <Justin.He@....com>; nd <nd@....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@....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@....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 "|". > > +} > > + > > +int kvm_arch_ptp_get_clock_generic(struct timespec64 *ts, > > + struct arm_smccc_res *hvc_res) > > Why isn't this static? > yeah, should be static. > > +{ > > + ktime_t ktime; > > + > > + > arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_PTP_FU > NC_ID, > > + hvc_res); > > + if ((long long)(hvc_res->a0) < 0) > > + return -EOPNOTSUPP; > > Really? What if the cycle counter is a full 64 bit value, as it is > *mandated* on ARMv8.6? It means that the counter is now invalid for half > the lifetime of the system. Not acceptable either. > > > + > > + ktime = (long long)hvc_res->a0; > > + *ts = ktime_to_timespec64(ktime); > > + > > + return 0; > > +} > > + > > +int kvm_arch_ptp_get_clock(struct timespec64 *ts) { > > + struct arm_smccc_res hvc_res; > > + > > + kvm_arch_ptp_get_clock_generic(ts, &hvc_res); > > + > > + return 0; > > +} > > -- > > 2.17.1 > > > > > > It is now obvious that the API between kernel and hypervisor is pretty > busted, and it goes beyond the 32bit support. I wish you paid more attention > to this kind of detail. Yeah, I will. Thanks Jianyong > > M. > > -- > Without deviation from the norm, progress is not possible.
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